Category Archives: Video Evidence Pitfalls

Compression Artifacts: Hiding or Adding Details to the Scene

Dear friends, welcome to a new video pitfall post! This time we’re dealing with a very sneaky part of video analysis: can we trust what we see? Sometimes, distinguishing the real detail of an object from that of an artifact is not easy. Today’s post will review some of the most common video artifacts and their possible effect on your work.

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Timestamps: Not Always Showing the Right Time

Dear friends, welcome to this week’s video evidence pitfall! In this post, we’re focusing on a crucial element of forensic video analysis: timestamps. Timestamps allow us to locate in time what’s shown in a recording, or reference an event to a specific moment in time. Although virtually all surveillance systems do record timestamps, you should be aware of several pitfalls in accessing and interpreting them, so keep reading!

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Receiving Video Evidence: Usually It’s Not the Original

Dear friends, welcome to another video pitfalls pill! Today’s post concludes our mini-series about using the “best possible evidence.” In the previous weeks, we always assumed you had control from the beginning. Today, we focus on a different yet widespread scenario: you receive the “evidence” from someone else and are asked to work on that. Want to know the undercover pitfalls in this situation? Just keep reading!

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Screen Capture: It’s Not the Evidence, It’s a Video of the Evidence

Dear friends, welcome! Here we are with one more post for the “best possible evidence” mini-series. In the past two weeks, we’ve seen that you should not film the display and that proprietary players often alter the original pixels. Today, we’ll close this mini-series talking about screen capture. We’ll see that, while being much better than filming, this approach still has its issues and should be used only as a last resort. Keep reading!

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Proprietary CCTV/DVR Players: Often Not Showing the Original Pixels

Dear friends, welcome! This week’s post continues the “best possible evidence” mini-series. Last week, we showed why filming the display is not good. This week, we address a related topic: can we trust proprietary players? You’ll be surprised by the number of pitfalls hidden in the bare playback of a surveillance video, so keep reading!

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Cell Phone Snaps: Bad Quality and Reliability

Dear friends, welcome to your weekly dose of fear! Starting from today, we’ll be addressing a fundamental issue, perhaps the most important in your video forensic workflow: using the best possible evidence. We’ll dedicate some posts to this important topic, covering the various pitfalls you may encounter. Today, we’ll see why using a mobile phone (or even a professional camera on a tripod) to capture footage is, well, not recommended. Keep reading!

Issue: Filming the Display Creates Awful Footage

Let’s start with a quote from one of our esteemed users:

The jobs I manage never get that far as we work with appalling quality footage in the vague hope of securing a conviction.

Well, it’s certainly true that, sometimes, there’s not much we can do. But in many cases, the “appalling quality” is due to how the evidence video has been acquired, or how the working copy has been produced. Let’s go practical with an example. Can you get this license plate?

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Color Fidelity: It’s Hard to Objectively Evaluate Colors on Video

Welcome to this week’s Video Evidence Pitfalls post, dear friends! Today we’re dealing with the reliability of colors in CCTV footage (and with any kind of digital images in general). Colors are an essential part of human perception, but can often be misleading in surveillance footage. Keep reading to find out why!

Issue: Colors Are Often Unreliable in CCTV Footage

As part of an ATM fraud robbery investigation, you are reviewing footage from two cameras in the same area. This is the image of the suspect as he walks away from the ATM.

He’s suspected of having visited another ATM of a bank nearby. So you review the footage of that camera as well, but… you don’t find anyone with a blue jacket and beanie hat. After syncing the clocks and checking frame by frame, you realize that it could be him:

But you also realize you will have a hard time convincing anyone about it. Why are the colors completely different?

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Playback Speed: If the Video Plays Too Fast or Too Slow, It Can Affect the Interpretation of the Events

Dear friends, welcome to our weekly Video Pitfalls post! Last week, we talked about the importance of a video’s time resolution (recording frame rate). Today, we’re dealing with playback speed, which is tightly related and also very important. Keep reading to find out why!

Issue: the same thing looks different at a different playback speed

As part of a burglary investigation, you are reviewing some CCTV footage of a parking lot. At some point, there’s an orange car that seems to act a bit suspiciously — it runs in one direction, then possibly realizes there’s no exit, and rapidly turns back. You even manage to see that the driver at the wheel acts quickly like he/she’s in a rush. Could that car be worth focusing on?

Notice that we are essentially basing the decision on how much of a rush the driver seems to be in. But what if the video played like this?

Everything is the same except for the speed: now the driver seems to be someone who just took a wrong turn and quietly turns back. And so the question now is: which of the videos (if any!) is an accurate representation of the actual event?

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Low Frame Rate: If You Don’t See It, It Doesn’t Mean It Didn’t Happen

Dear friends, welcome to this week’s video pitfalls post! When thinking of “video resolution”, we normally recall possible pixel matrix sizes (640×480, 1920×1080, and so on). This is the spatial resolution. A video however has a temporal dimension as well, with the ‘tempo’ relating to the speed at which the frames are captured and then presented. In many cases, this can be more important than spatial resolution. For this reason, we will dedicate this and the next post to this subject. Today, we deal with the recording frame rate, while next week we’ll talk about the playback speed.

Issue: If the recording frame rate is low, you are missing information

You are called to a bar where a scuffle just took place. Upon arrival, you listen to all the various witness and victim accounts and then the bar owner shows you the CCTV. This is what you view (we’re using a video from the “UnarmedcombatOnline” YouTube channel).

No matter how many times you play the video, you hardly understand how the guy with a black sweatshirt turns from standing to laying on the ground, and it does not match some eye-witness accounts. You decide to acquire the evidence (in a forensic manner) utilizing the device’s USB Export function.  Back at the station, or on your laptop, you view the evidence in Amped Replay. Carefully navigating the frames allows you to check thoroughly all the available information in the recording. By scrolling the gallery below, you’ll notice that in frame 2 the guy is standing, and in frame 3 he’s grounded. What happened in between? We don’t know.

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Perspective: Size Comparison May Be Tricky

Welcome, dear friends, ready for this week’s video evidence pitfall? Today we’re dealing with one video issue that often gets overlooked: perspective. It’s something we’re all familiar with, but in video analysis, it can play nasty tricks on you.

Issue: you shouldn’t compare the size of things at different depths

A robbery takes place and you get called. When you reach the shop, the owner runs at you yelling a classic statement: “I got him! I have a video!”. Indeed, there’s a video on the CCTV system and the suspect is there, as he walks into the shop (we’ve simulated a balaclava in the picture below). The face is disguised, but there’s good information about clothes. Then you think: well, I’m here in the shop, the suspect is close to the door, so why don’t I measure the height of the door to find out the height of the suspect?

Well, certainly measuring the door is an excellent step towards height analysis, but don’t take it too easy: that would just be the first step of a longer process. Indeed, you can’t directly compare the size of things at different depths because perspective makes farther things look smaller!

And it’s not just a matter of measurements: perspective affects the human view of an event. What you think you see may be affected by perspective: two planes in the sky may appear to be about to crash into each other when they are actually hundreds of feet apart. For CCTV, it may look as if an action or movement is one thing, but it is not in reality. Moreover, the perspective of the camera must be considered, and this is often very different from a witness perspective. Many cameras are high up and angled down, whereas witnesses will be at ground level and looking perhaps from a different angle. What one person sees may be very different from the camera’s view. 

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