Archive for the ‘Image Analysis’ Category

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.

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!

Forensic Photographic Analysis – Reverse Projection

Oct 25th, 2013 - Filed under: Blog,Expert Witness,Image Analysis,Photography

Some cases are unique – and this will describe one of those. In this case plaintiff retained me to determine if a photograph of a part was broken. The part was a water jet from a bathtub spa. The person using the spa was injured, and the reason proffered was that one of the legs that hold the jet in place was broken. The hotel personnel recovered the broken jet, placed it on a table and took one photograph of it. Later, the jet was lost before any expert could analyze it.

I was retained to determine if the leg of the water jet in the photograph was broken. The jet had three legs and the one that was believed to be broken was the one on the back side when looking at the photograph. Looking at the photograph, that leg appeared to be at a slightly different angle, but defense claimed that the leg was not broken and that the slight difference in angle may have been from the angle of the photograph, the lighting, the focal length of the camera lens, or simply the way that the jet was positioned on the table – or perhaps it wasn’t at a slightly different angle at all.

Measuring the angles of the legs to the front of the jet wasn’t possible because we had only one image and the leg in question was on the back side of the jet. A 3-D model couldn’t be built because there was only one photograph. But, a reverse projection analysis could be done. Reverse projection involves taking a new photograph from the exact same position as the original image, then one can have the data needed to make comparisons, make measurements, compare lighting, etc.

In this case, plaintiff provided me with a new, unbroken, water jet of the same make and model as in the original photograph. I placed it on a table in the exact same position as in the original. I set up lights to exactly replicate the lighting in the original, with all highlights and shadows matching. I set my camera into the same position that was used in the original photograph, and I took the picture. Next, I created an overlay of the two photographs. The result was conclusive – everything on the two water jets matched except for the one leg. The leg had to be broken on the jet in the original photograph, as there was no other explanation for the difference in the two photographs. The difference between the angle of the leg in the original photograph and in the new photograph were measured, and made part of the illustration.

 

Countering Bad Science

When attorneys get a copy of opposing counsel’s expert reports, sometimes they are quite surprised by what they read – it’s just bad science. And, in these cases they will then retain their own expert to counter, and possibly quash, the other experts opinion. I’ve been retained in numerous cases to do this, and I’ll discuss four to illustrate the benefit this has, and to help illustrate the kind of work that I do.

Recently, the Los Angeles District Attorney’s Office retained me because they suspected that the forensic video analysis and photogrammetry performed by the defense wasn’t based on science. I was provided with the security video from the business where the crime occurred, and with the report by the defense expert. In this case, the defense expert lacked training and experience in video analysis, photography, and photogrammetry (she opined on all three of these disciplines in her report). She also didn’t follow best practices in the acquisition of the video, and didn’t apply any standard method to the photogrammetry. I provided a report that the prosecutor presented to the defense attorney, and the defense withdrew their experts report.

In a civil case that I previously posted about, the defense hired a photography expert to photograph the scene of an accident to illustrate the level of illumination. This expert photographed the wrong area, used the wrong equipment, and presented photographs that misrepresented the area. I was hired by plaintiff’s attorney to counter his testimony. I went to the scene and photographed the correct area following best practices and properly illustrated the illumination of the area. In addition, I provided cross examination questions, and the opposing expert basically admitted that he just followed directions of others and didn’t know if he photographed the correct area in the proper manner. This resulted in a multi-million dollar settlement for the plaintiff.

In a military court marshal case, the prosecution brought in an expert in photographic comparison. In this case, the expert didn’t follow standard protocols in their comparison and reached a conclusion that was well beyond what could be reached. The defense team brought me in to challenge this testimony. I provided the attorneys with the information they needed to understand the science of photographic comparison and to illustrate the weaknesses in the opposing expert’s report. I also provided cross examination questions, which were used, word-for-word, and resulted in the prosecutor asking defense counsel why they didn’t make a Daubert challenge. The reason was that they believed the strategy of showing the problems of the comparison was stronger then having it quashed in a Daubert hearing.

One last case was one in which the prosecution in a homicide case created a video to illustrate the illumination of the scene. A large segment of it totally misrepresented the scene, and the defense retained me to counter that evidence. I visited the scene and I wrote a report outlining all of the reasons why the police video misrepresented the scene. The defense presented my report to the judge and she ruled that the segment of video could not be used.

These cases involve three different aspects of my work – video analysis, forensic photography, and photographic comparison – but the common thread is that I was retained in each case because these attorneys needed someone to counter bad science presented by opposing counsel. In each case, the attorneys retaining me weren’t planning to use an expert until opposing counsel did so, and they needed someone to counter the bad science that was being presented.

“I need to tell others about you!”

I met with an investigator on a case last week to discuss her need for Forensic Video Analysis in a homicide case. During out meeting, she asked about the other work I do in photographic analysis and photography services. When I finished, she asked me for a handful of cards so she can let other investigators and attorneys know about my services – she said, “I need to tell others about you!” She had already viewed my website, but some of the things weren’t as clear as they could be, and I realized that I could do a better job in explaining what areas of expertise I work in, and when attorneys could use my services.

This post will just introduce this topic, and I’ll follow-up with more specific examples in the coming weeks. Here are the basics of what I do, in the coming posts I’ll discuss each area with examples from cases to illustrate how this applies to a variety of criminal and civil cases.

To begin with, my expertise is in forensic photography, photographic analysis, and video analysis.

In photography, I provide witness perspective photography, illustrative photography, accurate photographs of evidential items, injury photography, etc. I have photographed scenes to show evidence, to measure distances, to show what someone saw, etc.

In photographic analysis, I provide clarification of images that may be too dark, blurry, from a bad angle, etc. I also provide authentication – to determine if the image is a camera original; and if not, to determine if it represents what it purports to (if it’s been Photoshopped). And, I provide comparisons – is the subject in one photograph the same as a known object (same car, same person, same make and model of valve, etc.). I can also help determine the relationship of subjects in the photographs to each other.

In video analysis, I provide evaluation of the video (what is happening, and are there factors that can be causing someone to misinterpret the events in the video); comparison – is the subject in the video the same as the known object; clarification – stabilizing shaky video, deblurring, adjusting brightness and color, etc.); illustration – following the action in the video, synchronizing multiple video files together, combining video with maps, timestamps, or other events to give a more complete picture of the events.

And, of course, I can evaluate the work of opposing experts to see if they have provided a correct view of the evidence.

My next post will discuss a case I worked for the Los Angeles District Attorney’s Office recently that resulted in the defense withdrawing all of their proffered video evidence.

Expert Credentials

One of the first things that I get asked for when an attorney calls is a copy of my CV. An expert’s CV can tell you a lot, but when looking at a forensic photographer, photographic analyst, or video analyst, how should it be evaluated to make sure that you are getting a qualified expert? What should you be looking for on our CVs?

This week I’ll address work experience. In the coming weeks I’ll also discuss training, certifications, testimony experience, and some peripheral issues.

One thing to note is that there is a huge difference between the worlds of photography and video in the commercial world versus the forensics world. When searching for an expert, I would want someone with experience specifically in forensic or legal aspects of photography, or video analysis. Look at their work history and how many cases that they work in forensics. Ask how long they have worked in photography, photographic analysis, or video analysis; and what percentage of their work is forensic based. For me, I’ve been working in photography for over 30 years, and in forensics for over 20 years. I have fifteen years experience at a police department in the field of forensic photography, image analysis and video analysis.

Interestingly, the world of civil law and criminal law have their differences as well. I remember my first deposition in a civil case some eight years ago. It was unlike anything I had seen in the criminal cases I had worked. Your expert should understand their role in your case as well as the procedures regarding reports, depositions, court, etc.

The bottom line regarding experience – make sure your expert is experienced in their discipline, and also in the forensic application of that discipline. The workflow of the commercial photographer or post production video editor may be excellent in their own field, but may fall apart in a forensic environment.

Next week we’ll discuss what training to look for in your forensic video analyst, forensic photo analyst, or legal photographer.

In Photography and Video – We Want the Original Images

It always surprises me how often retaining attorneys send me digital copies of scanned color laser prints of photos in PDF format, or transcoded video files to do an analysis. Sometimes these images resemble their originals – sometimes they are a far cry from them.

To do the best enhancement, analysis, or authentication possible, originals are needed. Exact, logical copies of digital evidence is fine if the originals are digital.

With photographs, the original is the digital file as it came from the camera, or the negative from a film camera. If it’s a PDF, it is not the original.

With security digital video recorders, the original is an exact copy of the original data recorded by the DVR. If the file plays on a standard DVD player – it probably isn’t the original.

Determining if the still photos or video files are originals does involve more than simply determining whether the video plays on a standard DVD player, or if the still image file is in a JPEG file format – but those are good starts.

Whether you are using an expert or not – start demanding exact copies of the original visual evidence in your cases – it will make a significant difference in what that evidence can tell you.

Reflecting back on 2009

When I think about the past year, and cases I’ve worked, training I’ve received, training I’ve given, there are a few things that stand out.

In the arena of cases, I had two unique experiences – A Daubert Hearing in 12/08, and Grand Jury testimony in mid-2009.

The Daubert Hearing was on image authentication (are the images real, and do they represent real people and real events). That hearing was U.S. v. Frabizio in December of 2008, and was one of the few Daubert Hearings on photography, imaging, or image authentication. It was an interesting case, as it was going to its third trial. I was retained by defense counsel to analyze and interpret the government expert’s report and findings. I provided information to the defense attorney on this report, and attended the Daubert hearing, and answered her questions on his testimony. With the limited number of Frye and Daubert hearings on forensic photography, forensic image analysis, or image authentication, it was an interesting experience to participate in this hearing.

The Grand Jury testimony was also on an image authentication case. In this instance, I was an expert witness for the government. I have testified in cases since the early 1990s, but this was my first time to testify before a Grand Jury. It was quite interesting, as there is no judge, no defense attorney, and the accused is not present, nor is a case detective. It’s the prosecutor, a court reporter, the members of the grand jury, and the witness. In this case, I was impressed by the professionalism of the prosecutor and the members of the grand jury – I can imagine a situation in which a system without the formality or presence of a judge, defense attorney, etc. moving toward chaotic – I was pleased that this was far from the case.

As to training I received, it would be a toss up between two classes I took in the field of photogrammetry. One was on reverse projection photogrammetry that I posted about earlier. The other was a class in using Photomodeler (a software application for applying photogrammetry) for close range photogrammetry, presented by Dan Mills of DCM Technical Services. Photogrammetry is taking measurements from photos, and there are several approaches to this technology. Unfortunately, there are very few classes available in close range photogrammetry or in reverse projection photogrammetry. I was fortunate to get excellent training in each in 2009.

Regarding training that I provided – it’s difficult to isolate any one specific workshop. But, I did have the opportunity to give four workshops in digital photography to the San Francisco Police Department in 2009. That agency purchased Nikon D700 cameras for their crime scene investigators and wanted each member to be trained in the use of that camera for crime scene and evidence photography. I was proud to be the trainer they chose to provide this instruction. We held four, three-day sessions, with eight investigators in each session. It was a pleasure to work with this agency and to see their dedication to providing their front-line personnel with the tools and training to do their job.

Lastly, another highlight of 2009 was being appointed chair of the Forensic Photography and Imaging Certification Board of the International Association for Identification. It is an honor to have been chosen to fill this position, and our board is working hard on several projects.

The last year was successful in many ways – looking back at a few of the highlights helps see where we are today and prepare for the future. I’m looking forward to more interesting cases and great training opportunities in the coming year.

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Reverse Projection Photogrammetry

Nov 22nd, 2009 - Filed under: Blog,Image Analysis,Photography,Video Analysis

The Law Enforcement and Emergency Services Video Association (LEVA) held it’s annual conference this week. I was fortunate to attend the two day pre-conference workshop on reverse projection photogrammetry presented by Richard Vorder Bruegge, Walter Bruehs, and Chris Iber, all from the FBI Forensic Audio, Video, and Imaging Analysis Unit.

Reverse Projection Photogrammetry is used to measure objects in a photograph or video. It can be used to determine if an individual could be excluded or included as a suspect based on height. In addition to using this method to determine the height of an individual in an image, I have used this technique to determine the position of objects in relation to their surroundings (after the objects were removed), the distance of safety barriers in construction scenes (after the construction was completed and the barriers removed), the size of cracks in a sidewalk (after the sidewalk was repaired), etc. from photos of those scenes.

The workshop covered issues related to the methodology and foundations of this technique. Any forensic image analyst or forensic video analyst who hasn’t yet had the opportunity to take this workshop should do so. It has been offered at the LEVA conference for two or three years, and also at the IAI Annual Conference.

Using Photoshop and Bridge for On-Screen Comparisons

Someone recently posted a question on the CLPEX website regarding on-screen comparisons. This question was specifically about fingerprint comparisons, but the method is the same whether comparing prints, footwear, vehicles, etc.

The first step is to determine which images to use (or eliminate). I frequently use Adobe Bridge for this. I set up Bridge in the Filmstrip workspace. If I need to compare two or three images to decide which I will use for the final comparison, I select multiple images and use the loupe tool to compare details. The loupe tool provides a 100, 200, 400, or 800 percent magnification of a portion of each image in the Preview panel. Just click on an image in this panel to activate the loupe, click and drag it to move it, click it again to close it. You can display one loupe on each image in the Preview panel, as shown here:

This image shows two images in Bridge with the loupe tool.

This image shows two images in Bridge with the loupe tool.

Once the images are selected, they can be opened into Photoshop for comparison.

If the images are of the same resolution and approximately the same cropping, then they can be synchronized for zooming and scrolling. Do this by choosing the “Zoom all Windows” and “Scroll all Windows” in the options for the Zoom and Hand tools. Now, if you tile the images side-by-side, and zoom, both images will zoom; scroll one, and the other will scroll as well.

A new blank layer can be added to each image and marks can be made on that blank layer to indicate various features. Multiple layers can be used to better separate different categories of features, etc. With the Extended version of Photoshop CS3 or CS4, the Count tool can be used to mark features.

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