Forensic video evidence has changed the way police investigations happen around the world.
Twenty years ago, forensic video was limited to analog video devices and had fewer technical challenges. Today, however, video evidence is involved in 85% of all criminal investigations and 94% of users experience challenges caused by the digitization of data.
This incredible growth of video has led to a democratization of video evidence – no longer is it feasible for a forensic video lab to exclusively handle all video evidence. While forensic video expertise may be critical in many investigations, video is also frequently reviewed by detectives, investigators, and others with minimal training. In fact, 70% of sworn officers interact with video evidence and 47% have minimal to no training.
Recent survey data shows that the more training an investigator receives, the more concerned they become about misinterpreting video evidence.
Why is that? Video evidence can be misleading and what you see may not always be an accurate representation of what actually occurred. In this article, we will share 10 important things every investigator should know about video evidence, which will help you know when it’s safe to review video evidence yourself and when to seek help from an expert.
Before we get started, you can test your knowledge on these topics by completing our forensic video quiz. It has 10 questions that are related to the 10 items in this blog.
Test Your Video Evidence Knowledge:
Answer Guide: 10 Things Every Investigator Should Know about Forensic Video
The following content contains more detailed explanations of each quiz question. Each of the 10 things below corresponds to a question in the quiz. We recommend completing the quiz before continuing!
(You can scroll back-up to continue the 10 question quiz).
1) Infrared Cameras change the colors in ways you might not expect
Infrared cameras are great for recording evidence in dark places. It’s important to know, however, that the black and white image of an infrared camera changes the color of things differently than you might think.
For instance, the image above is of a suspect who was involved in multiple home invasions – including one that involved a sexual assault of the woman who lived at the house. Investigators seized some gloves from a potential suspect and wanted to demonstrate the similarities to the glove worn by the individual on video.
Surprisingly, the pattern of the glove from the crime scene seemed much different than the glove in the video. This is because infrared alters the appearance of objects based on the material being illuminated, not the color of the object.
In fact, this glove with the yellow stripes is the exact same glove as the suspect was wearing. The back of the glove was comprised of multiple different fabrics, each of which resulted in a different degree of illumination. To prove it was the same glove, investigators wore the glove on another night in front of the same camera, and demonstrated that it was, indeed, a match.
It is important for investigators to understand the effect infrared cameras can have on the appearance of clothing and other objects and take that into account when conducting investigations.
2) Always Work with the Original File
Investigators frequently work with video files that have been converted from the original. For instance, a CCTV Camera might record to a proprietary .Dav file format that cannot play on an investigator’s computer.
It can be very frustrating when you cannot review a key piece of evidence. Officers who encounter a file they cannot play will spend an average of 83 minutes searching for a converter or player online.
Unfortunately, these methods are not reliably accurate. Proprietary DVR players and online converters can alter the video evidence by changing colors and shapes, inverting the image, dropping frames, and more.
For instance, this Use of Force case from Ottawa leveraged video evidence that was a screen recording of a proprietary player. While it may appear like the officers slam the suspect’s head into the ground, the capture process actually dropped frames and accelerated the appearance of the use of force in the video. The original file video file told a very different story. Always work with the original file if you can!
The court eventually threw out the altered clip, and instead reviewed the original file that provided a more accurate appearance of the use of force:
This is one of the reasons we created iNPUT-ACE. There are thousands of different file types and we know that Investigators need a reliable way to review evidence accurately.
3) Perspective Matters
Many lawyers have argued, “the camera doesn’t lie.”
If only it were so simple! When investigating video evidence, forensic video experts know that perspective matters. The placement of the camera and the suspect can influence our perception of events, which is why it is so important to always look for multiple angles and work to understand how the perspective changes the image.
For instance, check out this image of Prince William:
If this is all you saw, you would automatically think he was giving a rude gesture to the crowd or to the press. Fortunately, we have multiple camera angles and can gain a greater perspective:
As it turns out, he was holding up 3 fingers to explain something. As you can see, one camera does not necessarily tell the full story. Investigators should always seek to work with multiple sources, and sync the timing of video evidence so they can view things from multiple angles.
4) Video Evidence Does Not Speak For Itself
Another popular misconception is that “video evidence is a silent witness that speaks for itself.”
This idea was given a lot of credibility because of a Supreme Court ruling in Canada, and the ruling has been adopted in many places around the world. It was also determined during the days of analog video, when there was a lot more consistency in video evidence quality and playback.
Today, however, things have changed. Grant Fredericks, a certified Forensic Video Analyst, had this to say during an interview with Eugene Liscio,
“The concept that video speaks for itself is probably the most egregious introduction of an argument that I have heard, in court as it is testified today. This is because video does not speak for itself. Depending on how the video has been captured, colors may not present correctly, shapes may not present correctly. Oftentimes the video is not acquired accurately. Images will be dropped…So interpretation is critical. Video, like any other witness, can be misleading and must be interrogated.”
5) The Timestamp on Video Evidence May Not be Correct
Many cameras will place the recording time and date onto the evidence. This can be a helpful feature for investigators who are investigating a case with hours of video evidence for a crime that only took a couple minutes. If you know the time of the crime, you can quickly find the footage you need. It is also helpful if you have multiple cameras and want to sync the timing of them.
Unfortunately, the times displayed on cameras cannot always be trusted. User error, power outages, glitches, daylight savings, and many other features can cause the timecodes on cameras to be incorrect. In fact, it is not unusual to have a case with multiple recording devices where 1 device is correct, another is off by 20 minutes, and another is off by 6 hours.
You can learn more about correcting the timecodes with the video below:
In short, investigators should always measure the offset to real time. They can use this data to validate or correct the timing data that is displayed on the screen and automatically align them.
This can save investigators significant time and help move cases forward more efficiently.
6) Compression Can Remove Important Details
In movies and sports, people frequently review evidence that is incredibly high-definition. In the real world of video evidence, however, investigators must frequently work with lower quality footage.
The higher the quality of the recording, the more space it takes on a camera and computer. Many recording devices and converters get around this through the process of compression. It removes high frequency detail so that viewers can get a reasonable picture of events, even if key details get lost.
This can create significant challenges for investigators. For instance, the image below is from a case where a business in California was robbed at gunpoint, and the primary suspects were arrested that same day. Defense counsel argued that his client couldn’t be the same person as the suspect on video because his client has hand tattoos. As you can see in the video evidence, the suspect does not appear to have any tattoos.
In this case, the suspect IS the same person with the hand tattoos, but this particular DVR recorder removed a significant amount of “high frequency detail” in that specific area of the image. This effect can be measured by using the macroblock analysis tool within iNPUT-ACE – and is often helpful to articulate to a jury why images can’t be enhanced to the extent often shown in shows like CSI.
This is a frequent challenge with license plate footage as well. Compression can make the letters on the license plate extremely blurry, or even disappear. When that data is not recorded, then you cannot enhance it back. It simply doesn’t exist in the recording.
Although some compression occurs in the original recording, every time a file is converted it can add more compression. This is another reason why it is important for investigators to work with the original file whenever possible.
7) MP4 and WMV Files May Not Be the Original
When forensic video specialists are given an .mp4 file or .wmv file from a CCTV system to review, they immediately ask, “is this the original file?” Both .wmv and .mp4 are popular video file types and can play on most devices, so it may seem like a good thing when you’re trying to investigate video, however, it often means it is a converted file and not the original.
While some cameras do record video in an .mp4 format, most do not. For instance, we were once asked to “enhance” an .mp4 video that featured a slip and fall that was the basis of a lawsuit.
When the .mp4 file was played, it was obvious that many frames had been dropped from the conversion process. A technician working for the attorney’s office thought it would be helpful to convert the file into a playable format, but the converted file dropped 59 out of every 60 frames and dramatically altered the evidence. When we asked the attorney for the original file, they did not want to provide it because no one could play the original file.
When they finally shared the original file, it was played through iNPUT-ACE and immediately all of the frames were available for playback, the video was no longer inverted, and the aspect ratio was corrected. The actual events became much more evident, and the lawsuit was quickly dropped.
If you are given a .mp4 file or .wmv file, be aware that it is may not be the original file, and always ask for the original if it is possible.
Note – some in-car cameras and body cameras do record directly to .mp4, but we have no known systems that record directly to .wmv.
8) Check the Aspect Ratio
Aspect Ratio is “the ratio of the width to the height of an image or screen.” Older “tube” televisions had a 4×3 aspect ratio with the width of the screen being 4/3 of the height. Today, most television screens and monitors are a wider format, like 16×9.
While many surveillance systems record files that are intended to display at 4×3 or 16×9, they often record at alternative sample aspect ratios. For examples, see below image from this webinar on Aspect Ratios and Resizing.
Notice the common 2CIF resolution is 704×240. This produces files that are recorded at “half resolution,” which stretches the appearance of objects. The image below, for instance, is only half as high as it should be. This makes the vehicle appear to be shorter and wider than it actually is.
Before the video should be played in court, the field should be converted with the proper tools that can correct these issues.
And of course, we’ve said this multiple times, but investigators need to ensure they start with the original file. Many free converters and some DVR players will alter the aspect ratio of an image, distorting the shapes and making it more difficult to understand or determine what is happening.
9) DVRs that record proprietary video may still play the video incorrectly
Many CCTV camera systems record proprietary video files that can only be played with the special video player that is also made by the same manufacturer who created the recording device.
Many people assume that if you want to play the video correctly and see what really happened, then you should play the proprietary file through the corresponding proprietary player. Unfortunately, time and experience has consistently demonstrated that the proprietary players often misread their own video files!
To ensure accurate video playback, always use professional video investigation software like iNPUT-ACE. The iNPUT-ACE team consists of certified forensic video analysts/technicians and former law enforcement officials who continue to conduct active video-centric investigations and analysis and are constantly validating the accuracy of our decoders
Because our team is at the forefront of practically applying video from the crime scene to the courtroom, we are constantly progressing our software to meet the evolving needs of public safety around the world.
10) Wide-Angle Lenses can Distort the Appearance of Distance
Body Worn Cameras (BWC) are among the most common sources of video evidence during video investigations. It’s a very useful tool for investigators, a New York agency has several years of data showing that they close the highest percentage of cases when BWC is involved in the incident.
BWC typically record with a wide-angle lens so that more evidence can be seen, but this lens also distorts the appearance of distances. It is important for investigators to understand that “Objects in the mirror may be closer than they appear.”
This comes up regularly in Use of Force cases where the suspect may seem further away and smaller than he or she actually is. For instance, in the image above, the suspect may seem 15-20 feet away, but he is actually only 10 feet away and may pose a greater threat to the officer than the lay person may assume from the image.
Want to learn more?
If you’re an investigator who wants to learn more about video evidence, we strongly recommend the course, Video Examinations for the Police Investigator.
Investigators who successfully complete this course will improve their video literacy, gain an awareness of video evidence limitations, and become proficient in executing industry-standard investigative techniques while appreciating the need to “stay in their lane” and accepting when to seek help from an expert.