Developing Rules of Thumb in Video and Photographic Analysis

Sep 10th, 2015 - Filed under: Blog,Image Analysis,Photography,Video Analysis

A common request for those of us who work in video analysis (whether privately or for a law enforcement or government agency) is to enhance a license plate or compare the person (face, article of clothing, etc.) in a video to a photograph of a person. When is there adequate information to expect that various methods of enhancement may generate value? I develop rules of thumb for these situations.

I think it makes sense for analysts to experiment with files to develop their own rules of thumb as well. In this post I’ll share some of the methods I’ve used to develop my own rules.

License plates. The first thing I did regarding license plates was to determine how many digits may be in a plate, and what the average, minimum number of pixels required are to display the plate. If the state or country uses seven digits, and we consider that most digits require a minimum of three pixels horizontally and one pixel between digits, then a minimum of 27 pixels can, theoretically display most letter and number combinations. If the plate has a couple of W’s and M’s then 27 may not be enough, and if it has fewer digits, or if all the digits are the Letter ‘I’ then fewer pixels would suffice. So, that’s a starting point, but there is more to this.

Do real world examples match this theoretical approach, and are there other things to look for that may be of value? How do compression, lighting, and recorded tonal values affect this? This is where one needs to experiment. You can either take high quality photographs of license plates, or download them from the internet. Then, make multiple versions of these at a variety of pixel resolutions, at a variety of compression settings, at varying degrees of reduced contrast. Save these files and begin analyzing them (starting with the worst) to determine what observations you can make at what settings, sizes, etc. For instance, can you determine the colors in the plate at 20 pixels wide? What resolution enables you to determine the difference between a dealer plate and a standard plate? How many tonal values are required before you can distinguish various characters? As you do this analysis, take notes and see if you find consistency from one plate to another. Start to make other observations – such as when can you differentiate between a ‘5’ and an ‘S’ or a ‘1’ and an ‘I’?

Follow this same approach for other items. For faces, I do a few things. I download mug shots of celebrities, save photos of myself, family, colleagues, and friends, and download random photographs of strangers. As with the license plates, I save multiple copies at varying resolutions, degrees of contrast, compression settings, etc. Then I make my observations. How small of an image shows me an accurate rendition of hair and skin color? When can I determine eye shape or nose shape? When do blemishes begin to show? How about tattoos? How much contrast is needed for a tattoo or blemish to show?

By doing these experiments, we can each have a fairly good idea of what level of resolution, quality of lighting, degree of compression, etc. is necessary to get what level of value from the images we work with daily. We can have some rules of thumb, and we can provide realistic expectations to our colleagues or clients when they bring us images. We can easily explain not only what those realistic expectations might be, but also why, and show them examples to help them understand what limitations may exist.

Raw vs. TIFF for Digital Camera Capture

Jun 18th, 2015 - Filed under: Blog,Fingerprints,Photography

Someone from a major law enforcement agency recently asked me for my opinion regarding the best choice between capturing raw or TIFF files from a digital camera. His concern was that the raw workflow is slower, results in duplicate images (the raw original files and the working TIFF files), and that the raw files are proprietary, and therefore different for each camera brand. Please note that this is only about digital camera capture – not about captures from flatbed scanners.

His concerns are all understandable, but I believe there is a simple answer to each of them.

Is the raw workflow really slower? If a raw file is opened using Adobe Camera Raw and adjustments are made to the image, then opened, it is then in Photoshop and ready for additional processing. With a TIFF file, one skips using Camera Raw, but the time spent processing either file is about the same. But, you can also synchronize the Camera Raw adjustments across multiple raw files with a single mouse click, and then use the Image Processor to convert these to TIFF files for working copies. This gives the speed edge to the raw files.

This leads to the issue of creating duplicate files. But, is this a real issue? The original file that is archived needs to remain unchanged – regardless of file format. When working on that image, the analyst may be making adjustment layers, applying smart filters, sizing the image, etc. That file will be saved as a working file – creating a ‘duplicate’ regardless of the original file format. Since the original raw is significantly smaller (requires less storage space) and contains substantially more information than the camera-generated TIFF, the win goes to the raw file again.

Raw files are proprietary. This is true, and has caused problems when camera manufacturers have stopped supporting raw file formats in the past. The solution to this is the DNG file format. This format is a container that can embed the raw file as well as the information needed to open it, thus providing a more universal file format that will last into the future. DNG files can be automatically generated as the files are downloaded from the camera. TIFF files are also fairly universal – although, if they contain proprietary data, such as Photoshop Adjustment Layers or Smart Filters, then they can only be opened by Photoshop, for example, thus making them proprietary as well.

Raw files are also considered to be a ‘digital negative.’ This is because one cannot make adjustments to the raw file and save the adjusted raw file. Instead, the adjustments made to raw files are sets of instructions that exist either as a separate, XML file, or within a database. When the raw file is opened, those adjustments can be disabled and the original image viewed as captured. Although following best practices with any file format will preserve the original captured image, the raw file format is like putting an extra deadbolt (or ten) on the file.

What about image quality? A raw file is high-bit (usually 12 or 14 bits of information) but a camera-generated TIFF file will be automatically converted by the camera (compressed, downsampled) to 8 bits. The raw file has no embedded color balance or color space, but the TIFF has both. These three things (smaller bit depth, embedded color balance, and embedded color space) make it so that the TIFF will lose quality more quickly with image adjustments than the raw file. And, the raw file will contain more tonal values by orders of magnitude. The camera-generated TIFF image is much more like a camera processed JPEG than a raw file. A strong advantage goes to the raw file.

Next, let’s consider the SWGFAST recommendation regarding images of fingerprints being captured and preserved in a lossless file format. The intent of this recommendation is to enable us to get the best capture possible, and preserve the most information, from our equipment, but I think it leads to some misunderstanding.

A TIFF image, that is generated in-camera, is uncompressed, so it meets this recommendation – but it is actually much more like a camera-generated JPEG than like a raw file. There is quite a bit of in-camera processing that has taken place to generate that TIFF as mentioned above. A large amount of the image data is thrown away by the camera when creating the camera-generated TIFF file – these same processes occur when the camera generates a JPEG image! A camera-generated JPEG image at the camera’s highest quality setting will be virtually indistinguishable from a camera-generated TIFF file – except that the TIFF file will be substantially larger.

Why is an 8-bit TIFF file larger than a 12 or 14 bit raw file? The digital camera doesn’t actually record color information. Instead, it records brightness values for each pixel position. The CCD or CMOS chip is covered with red, green, and blue filters, with each filter position following a specific pattern. The raw file simply records the brightness value of each pixel, and later applies the color interpolation only when the image is opened with a raw file converter, such as Adobe Camera Raw. But, the TIFF file has already applied this color interpolation, so each pixel needs to be described as three separate values, or channels. To measure the number of bits needed to store an uncompressed file, just multiply the pixel width by height, times the bit depth, times the number of channels. Although the bit depth of the TIFF file is less, the number of channels is tripled, making an uncompressed TIFF about twice the size as an uncompressed raw file, even though the raw file contains much more information, and will hold up to a significantly higher amount of image processing.

This leads to the question of whether a JPEG file is really as bad as we have been led to believe. I’ll address that issue in a future post – but I personally prefer a raw workflow and think that the benefits of shooting raw are significant, and that there is no real cost.

The Value of Forensic Photography Certification

Jun 2nd, 2015 - Filed under: Blog

When I first started my career in forensics I didn’t recognize the importance of certification. My assumption was that my education, experience, training, and work spoke for itself. I was confident in my ability and didn’t think that having a certification would make me a better photographer. Later I changed my mind, and I believe that there are three things that show the value of certification.

Self Assessment: Having confidence in one’s work is great, but how do we know that our self-assessment is accurate? How do we know that we meet the standards of our profession? How do we determine that our level of knowledge and skill is what our field requires? By meeting the requirements and standards set by a valid certification program, we know that we are doing a competent and professional job.

Professionalism: It’s all too easy to approach our day-to-day duties as routine. We’ve photographed hundreds of crime scenes, hundreds of pieces of evidence, hundreds of fingerprints, footwear impressions, etc. We can become stagnant and do everything with a bit less professionalism than we did when we first started. Certification requires that we present each assignment with everything done right and in a professional manner. By meeting the standard for each assignment in the practical exam, we show that we have the skill to nail each and every photograph that we take.

Courtroom Testimony: Sure, we can meet the requirements to testify about the photographs we take without much difficulty. And, with a given amount of education, training, and experience, we can testify as an expert in the field of photography. But having the certification shows the presiding judge and the jury that you have gone beyond these and voluntarily been tested and met the requirements for certification. Court qualifications are met more easily and the weight of your opinion and evidence is increased.

Career: When I started in forensics, it was rare for an agency to require a college degree. Now it’s common. In fact, many agencies offer extra pay for those certified in their discipline, or make it a requirement for some positions or for advancement. In the future, I expect certification to be required for most forensics positions as well as for courtroom testimony.

There are many more points that can be made about the value of certification. Eric Johnson and I have developed a five day workshop titled, Forensic Photography and IAI Certification Prep Course. If you are considering seeking the IAI Certification in Forensic Photography, our course can help you prepare. If you just want to hone your skills in forensic photography, our course can help you with that as well.

George

PS: Photography is a part of virtually every forensic discipline. Our course, and this certification, are beneficial to all forensic professionals!

SoCal Technical & Scientific Photography and Imaging Group

Apr 21st, 2015 - Filed under: Blog

I’ve just launched a new MeetUp Group in Southern California for those involved with technical and scientific imaging and photography.

The purpose of the group is for those of us in technical disciplines to share ideas, techniques, processes, and solutions with each other. Imagine the software engineer, bio-medical photographer, and forensic photographer discussing solutions to easily calibrate the size of an image. Or the astrophotographer and photomicroscopist sharing image registration and stacking solutions. Does your discipline use best practices and standard operating procedures – well, the art conservation community have a great book on this topic, many forensic labs are willing to share their SOPs, and the FDA has restrictions on the biomedical community. Perhaps we can all share some of this information with each other and we can all benefit. Know a great lighting set-up for dark field illumination or coaxial lighting? Share it with our members at one of our meetings.

Right now the group is limited, physically, to Southern California. If there is enough interest I will figure out a way to expand it. My original intention was to create an international association, but I realized that was too ambitious to start with, so I’ve started with this. However, MeetUp does have a Discussion section that I plan to begin utilizing soon – and that may be a place to come and share information if you are not in Southern California.

But, if you are in SoCal, and your work (or study, or interests) involve photography or imaging in a technical or scientific aspect – please join the group and attend our meetings.

Forensic Rulers

Dec 23rd, 2014 - Filed under: Blog

I was looking at the website of a forensic vendor last week and browsing through their selection of rulers, and it prompted me to write to the vendor and make some suggestions. But, it also caused me to remember when I first met Larry Stevens, who, at the time, sold rulers for the Oregon Rule Company. Larry had a booth at an EPIC (Evidence Photographer’s International Council) conference and demonstrated his rulers with an enthusiasm that was contagious! You would think that he was the Ginzu Knife sales person on the old television commercials. Oregon Rule had some innovative designs, and they can still be found on their website. But, almost all the forensic vendors continue to sell the same old products that have been around since the 1980’s and before.

So, what do I think is wrong with today’s choices of forensic rulers?

1) The first problem is that most have metric scales. If I lived in Europe, that would be perfect; but since I live in the United States, it makes no sense. If I photograph a knife blade that is 16 cm in length – what juror knows how long that is? But, if my ruler shows that it is 6 1/4 inches, every juror knows that size. There is nothing more accurate or precise in one system or the other, but there is something much more recognizable in one over the other, depending on where you live and who your audience is. My audience is in the US, and eventually is a group of jurors.

2) The color of the rulers. Most of them have either a white background with black writing; or a black background with white writing. These provide good contrast and don’t reflect stray color into the image, but there aren’t the best color choice either. The white ones can become overexposed, bloom, and become difficult to read. The opposite can happen with the black. And, even worse are the rulers with bright color backgrounds like the highly saturated blue or the fluorescent yellow. These are difficult to look at, much less read – and take away attention from the subject. But, even worse, they may reflect their own color into your scene! The best color choice is a light, neutral, gray background. This won’t be likely to bloom, it won’t contaminate the image with it’s own color, and it can be used to white balance your photograph. I’d suggest something like the neutrality and lightness of the WhiBal card – these are spectrally neutral, and light enough to be able to easily read the printed information.

3) Replace the ABFO markings. I don’t know when ruler manufacturers first started using the circle with the plus sign in their designs – but I don’t know anyone who actually uses it! The concept behind it is great – use the circle to correct any perspective distortion in the image. But, in practice, it really isn’t done, and it really isn’t easy. But, what could be easy is if a manufacturer designed a symbol that could be used to easily correct perspective distortion through software. Imagine a Photoshop Plug-In that would detect the symbol and apply the correction, and perhaps also calibrate the image size. Chris Russ of Reindeer Graphics and I have discussed this in the past. I don’t know if he’s put any time into such a project – but someone should.

4) Add a place for erasable information. I’d love to write my name (as the photographer), the date, the case name, and the location onto the ruler. I’d love to use a fine point marking pen, and then be able to wipe that info off the ruler to write new information for my next case.

5) Accessorize the rulers! There are two ideas that I have – but I’m sure there are other ideas. First would be a snap-on arrow. This would be used when I want to include an arrow to point to north for orientation in my images. It would be removable because I certainly don’t always need it. The second is to create Tee and Ell Connectors. These could be used to attach straight rulers together to get T- and L- shaped rulers. No more carrying multiple L shaped rulers – just carry a few straight rulers, and use the connectors to assemble them how you want. You could even make a rectangle fairly easily.

Of course – all of this would only be any good if the manufactures would take excellent care in choosing the quality of their materials, the precision of the manufacture, and the quality control. I’ve thrown away rulers because they have been inaccurate or have obvious inconsistencies in their line thicknesses.

So, those are my ideas for the simplest of rulers. I’d love to see a manufacturer take these ideas and give us something better than what is currently on the market. I’d like to see forensic vendors insist upon something better. And, I’d love to see the end users think about these issues when making their purchases and placing their ruler in their photograph.

Image Authentication Kickstarter Opportunity

Dec 21st, 2014 - Filed under: Blog

I recently read about this on Jim Hoerricks’ Forensic Media Analysis blog. It’s a Kickstarter project to develop an image authentication application. I made a pledge and am posting this to encourage others to also do so. Here’s why.

First, I don’t have any vested interest in this (other than the pledge I made), and I don’t know the developer. Also, I don’t expect that this project will produce anything that isn’t already available with other software. I currently have Amped Authenticate and FIAS, and love them both.

But, what I am hoping is that by supporting this project, it will encourage more development and research into image authentication. And, what I’m afraid of is that if this project fails, then it will discourage this developer, as well as others from continuing development in this field. In addition, for just a $30 pledge, you will walk away with a piece of image authentication software. That’s the best deal any of us are likely to see in a very long time.

So, for a pledge of $30 (or more if you are so inclined), you get a copy of an image authentication software application, you (at minimum) encourage one software developer to continue doing research and development in this field, you avoid discouraging him, and others, from continuing development in this field, etc. It really seems like one of those win-win situations to me.

And, if you are looking for a mature and complete authentication, don’t forget to take a look at both Amped Authenticate and FIAS – both are excellent applications that offer a very complete set of authentication tools.

Featured on f/stop spot

Dec 14th, 2014 - Filed under: Blog

I was recently interviewed by Steve Paxton, a photographer in Washington state, for his blog at f/stop spot. Steve is a talented photographer who does work ranging from street photography to weddings.

In his interview, he asked me about several things, from what I do as a forensic photographer and image analyst, to how one can find a job in this field.

It’s interesting to think about these things and think about the path to my career versus how one might plan a career in forensic photography or forensic image analysis today. My path was a bit accidental, but has been very rewarding. Government jobs in forensics have always been competitive, but are more so now then ever before.

Although I didn’t discuss specific cases in the interview, I thought about many specific cases during the course of it. I plan to post about some of the cases I’ve worked in the near future.

Frye Hearing

Nov 10th, 2014 - Filed under: Blog,Expert Witness,Testimony,Video Analysis

Last month I testified in a Frye Hearing in Los Angeles. The Office of the District Attorney retained me to challenge a defense expert in a case that involved both Forensic Video Analysis and Photographic/Video Comparison.

That ‘expert’ has testified 25 times in the past, but has had no training in Forensic Video Analysis or in any Comparative Science. His work experience was only peripherally related to video analysis. He does not have any certifications in video analysis, photographic analysis, or anything related to these fields.

His methods in video analysis and in comparisons are not considered best practices by any peers, any forensic organization, or in any publications. Additionally, his comparison method is a method that the Facial Identification Scientific Working Group (FISWG) specifically states is not appropriate for comparisons. Further, he identified artifacts as being features, which the Scientific Working Group for Imaging Technology (SWGIT) points out is something that should not be done.

Because this other ‘expert’ read my report prior to the hearing, he was able to rehabilitate himself somewhat. His testimony indicated that he did things differently than his report indicated. He had trouble answering any direct questions – even those asked by the defense attorney. He frequently rambled in his answers with the attorney having to ask the question again or otherwise bring him back on track. He claimed that he used methods that no one else uses and that he therefore has no peers in this field.

I took the stand in this hearing and listed the training that is available, the certifications that are available, the organizations that publish guidelines and best practices documents. I showed that the other ‘expert’ had no foundation for any of his work. For example, he stated that his measurements had a specific margin of error, but never explained how he derived that margin of error. The image had significant motion blur (from both camera and subject movement), was a night shot from a cell phone camera, was of low resolution (the head size was 30 X 30 pixels), the cell phone used a rolling shutter, it was a night image, etc. In addition, this ‘expert’ then rotated this poor quality image, causing further degradation. With the CCTV footage, he used a PDF file that he was provided with, and there is no indication that he ever asked for the original file. He did not recognize the aliasing artifacts in that image that were caused by the low resolution and also because the video was interlaced.

The result? The judge came half-way, and stated that he could not testify regarding the comparison, but that he could testify about the video quality. Since that wouldn’t benefit the defense (who he was working for), he didn’t testify at all.

But, what is the future for that expert? He is listed on the Los Angeles Superior Court Panel of Approved Experts. This means that when a defendant in LA County wants an expert, they can choose one from the list and ask the court for funding. This expert stated that he has worked over 150 cases and testified 25 times. The next public defender who chooses him may not know of his history – this wasn’t his first Frye challenge. He’s been admonished by a judge for talking to jurors in the hallway in one case, and also for giving a sentencing opinion while on the stand! He invents theories and rambles on and on to try to support them. And, he is still on that Panel of Experts.

What is the criteria to be on the Panel of Experts? One has to complete a form. It is one page. And, one has to attach a CV. I don’t know how one is approved. There are no references asked for, so it’s likely that none are checked. There is a space for Licensing information – but many expert fields don’t require licensing – although there may be certifications (but there are no questions about certifications, or other qualifications). Once one is on this list, I don’t think there is ever a review. I’ve never heard of someone being dropped from the list.

So, the next time a public defender in Los Angeles needs an expert, he or she will take a look at the approved list and see this expert’s name. That public defender may not have the time to search out the background of that expert, but instead may just assume that because he is on the list, he must be competent. It is a frightening situation. I hope that the LA Superior Courts will review the criteria used for placing (and retaining) individuals onto their experts panel.

In closing this post, I’ll point to a post on this topic by Jim Hoerricks. It’s a great read, with a bit more detail about the members of this panel in the category of video, audio, and image analysis.

LEVA’s FVA Certification Process

I received my Forensic Video Analyst Certification from LEVA at their annual conference last week. A few weeks ago I posted a survey about certifications in FVA and Photography. The responses to that survey showed quite a number of misconceptions. And, since LEVA’s process is fresh in my mind, I decided to post about their process.

First, let me state that I also hold certifications in Forensic Video Examination and in Forensic Photography and Imaging from the International Association for Identification. Their process is also an excellent one, but I am specifying the LEVA certification today.

One misconception about LEVA that I’d like to clarify is that it is only open to law enforcement personnel. This isn’t the case. I didn’t even join LEVA until I was no longer working for a police agency. LEVA has an associate membership for non-LE. Their conferences, classes, and certifications are open to non-LE. They do charge more to non-LE for most of their classes (which is a policy I disagree with) but they are all open to civilians.

The process is a long a challenging one. They require that an analyst works in the field of Forensic Video Analysis, has had 88 hours of training in FVA, and passes a board. Actually, the 88 hour requirement is more than 88 hours, as one has to complete and pass the LEVA Level 1, 2, and 3 classes which total 120 hours plus the LEVA Photographic/Video Comparison course. That’s an additional 40, which brings the total to 160 hours.

With each of the LEVA courses, there are a minimum of two tests – a written test on the material covered, and a practical test. In some cases there are additional tests, for instance the Level 2 course also has an oral test. Each course is chock-full of great material that anyone working in FVA should know. Level 1 covers the foundations, which include basic technician practical exercises, a section on ethics, another on basic legal aspects as they apply to video evidence, issues about basic terminology from the definition of Forensic Video Analysis to spatial and temporal compression, pixel aspect ratio, file formats and codecs, etc. This class is a big surprise for many because some people fail. LEVA makes it very clear that tests will be given, and that some will fail. The same holds true for every LEVA class – these courses are not excuses to get out of town and socialize – they are serious educational opportunities, with full days of serious classes, and with evenings spent in study groups. Level 2 primarily covers issues with DVRs and NVRs, and using best practices in the acquisition of video evidence. In Level 3, the participants are given a case in which they have to properly acquire the evidence, perform a full analysis, write a report, and present the case in a moot court. Most of the students work in the evenings on their cases, as well as the allotted time during the day.

Once one makes it through these courses, one feels a sense of accomplishment. After also completing any remaining training, one needs to submit a case to the LEVA certification board. Applicants are provided with a mentor who can help guide the applicant through the process, review the case, make suggestions, etc. Then, the applicant submits that case to a gatekeeper who reviews the case and determines if the case meets the criteria for boarding. If it does, then the candidate meets before the four-member board for approximately 40 minutes during the LEVA Conference. The board members consist of three analysts and one attorney. The board members can ask questions about the case, your methodology, your conclusions, technical issues, and also about things that you should know as a certified forensic video analyst. One feels pressure at this boarding, and the candidate is well aware that the board members know the answers to the questions that they are asking – one cannot fake their way through this process.

This year there were eleven candidates for certification. Six passed, the other five have the option to try again in a year.

This process is a long and challenging one. Completing it is an accomplishment in itself. I learned something in each and every course I took and through the boarding process itself. Participating was a privilege. Passing was an honor. This certification has a lot of meaning, and I am proud to have earned it.

I’ll close this post by thanking all of those who have given of their time to LEVA as certification board members, executive board members, instructors, lab assistants, etc. The field of forensic video analysis is better because of you. Thank you!

LEVA Level 3 Training

I just got home from taking the LEVA (Law Enforcement and Emergency Services Video Association) Level 3 Course at the University of Indianapolis. It’s been a couple of years since I’ve taken a class through LEVA and this class reminded me of how great their training is!

I have previously mentioned the importance of training, and I try to attend at least one course every year. The Level 3 Course is very appropriate for all forensic video analysts to take, and it properly requires prerequisites of Level 1, 2, and the Video/Photographic Comparison classes. There is some quick review of concepts from those workshops, updates on legal cases involving video evidence (a case I worked on was discussed), then we are given a previously adjudicated case to work. We get two-and-one-half days to analyze the evidence, form an opinion, write a report, and prepare court charts. Then the testing begins. Our cases are presented in a Moot Court, with a Forensic Video Analyst (Scott Kuntz) and a Prosecuting Attorney (Jonathan Hak) questioning our evidence, our techniques, methodology, etc. There is also a written test, a practical test, and a comparison exercise to complete.

The course is complete, testing in most areas that a Forensic Video Analyst should be proficient in. The instruction is excellent. The casework is very representative of what I see in my business. And, the feedback is valuable. Any Forensic Video Analyst who hasn’t yet attended this course should sign up for the next offering as soon as they can. Any Forensic Video Analyst who hasn’t had any LEVA training at all is doing their agency or their clients a disservice.