The Reliability of Image Representation

It’s been a long time since I posted here.
I am the first one to admit that I can get a little passionate about Forensic Video Analysis and CCTV Investigation, and my frustrations with various aspects of this niche field of forensics can take their toll on my wellbeing.
Sometimes you just have to take a breath, rather than bang your head harder on the brick wall.

There are though a handful of other analysts who have continued to shout about certain issues for some considerable time. Unfortunately, we often seem to get drowned out and the problems get lost and ignored within the legal system. It was a refreshing change therefore a few weeks ago, to see and hear from one of those respected colleagues on the UK’s Channel 4 news.

It is clear that the news item has probably been heavily edited, cut down and slanted to concentrate on facial analysis BUT there are some important takeaways from this and things that we, as analysts, must consider.

Firstly, let me make this clear. CCTV is not putting innocent people behind bars.
Misunderstanding, incorrect handling, poor analysis and biased presentation will put innocent people behind bars. It’s not CCTV’s fault!

Second.. the images and comparative analysis displayed in this video leave a lot to be desired and cause damage to the role of the Forensic Video Analyst…but worryingly, I have seen worse.

Professor Gillian Tully, right at the outset states, “When it comes to the interpretation of CCTV Images, its difficult for us at the moment to have the assurance that it’s done properly across the board…” She then goes onto the fact that people and organisations do not meet the required standards set by the Forensic Science Regulator (FSR).

I am not going to get into the huge mess surrounding the initial setting of the FSR’s guidance in the UK.

I am not going to get into the conflicts between the FSR’s guidance, the training delivered to most police organisations in Forensic Video Analysis, and then the guidance documents published by the National Police Chiefs Council.

I am also not going to get into the ISO accreditation of video units and private service providers and the difficulties this has caused…

We have to go all the way back to the start, and clearly define what a person should do and what is their role to the court.

I have been lucky, or unlucky in many cases, to review lots of Forensic Video and Image reports and there are some constant problems. The most common is an unclear definition of what that person’s role is within the investigation.

In any case where video evidence is to be used, whether that from CCTV, Cellphones or Body Worn Video, an analyst must ensure and report on the integrity of that video, the authenticity of that video and the reliability of the image representation.

Why is an expert in video required to do this? You all watch the TV, you all watch YouTube. The latest viral video of a dog skiing is completely different, however, to a piece of footage recorded on a CCTV system that could result in an innocent person being convicted of a crime they did not commit.

Regardless of the task or question being asked, the analyst has a duty to the court to assess and understand the evidence.

The analyst’s first responsibility is to identify any changes in the image since the time it was first created. This ensures the integrity of the exhibit. Any changes must adhere to a scientific workflow and therefore be repeatable, reproducible and explainable. Any item produced as a result of a change will differ from the original and, as such, will be a new exhibit. Any undocumented changes must be disclosed as these will affect the integrity of the produced item.

The second responsibility is to ensure authenticity. Any item must be a true and accurate representation of that which it purports to be. The video may not be authentic in its original state. The capture and encoding of the video may have changed the shape, dimensions, speed or colour, and consequently, anything in the scene would suffer from this incorrect view. Authenticity therefore not only relates to the identification of fabricated evidence, either through malcous manipulation or incompetence, but more commonly to the method of aquisition. In these cases, authenticity can often be restored through restoration and enhancement.

This is where the third responsibility comes in. Ensuring the reliability of the image representation. This is often termed the scientific stage, as processing, reconstruction, testing, restoring, enhancing, collating, annotating and presenting video evidence must adhere to a scientific workflow. If those are followed, and any required peer review completed, the produced item or presented fact should be reliable.

It is not the analyst’s role to form an opinion as to an item, or a mark. It is an analysts role to inform the judge or jury that the item or mark constructed within the image is reliable and can be trusted.

It is not the analysts role to make up terms and use incorrect, unscientific procedures.

It is not the analyst’s role to fit the narrative of those who are employing them.

Comparative Video and Image Analysis can be extremely time-consuming work…. but also very frustrating. Most CCTV used is not installed for the purpose it is being used for and, as such, identifying and documenting the limitations is key for transparency and trust.

When the analysis starts with the identification of the facts, it is easy to perform unbiased analysis and, if necessary, report that an object or views representation is unreliable.

And this workflow is not just for comparative analysis. Timelines, storyboards and the tracking of persons through scenes can all be presented incorrectly with unreliable visual information if the original data is not understood and analyzed correctly first. The staged disclosure of video exhibits is also of key importance to reduce unconcious bias.

An analyst is there to identify the facts in the video or image. There should be very little subjective interpretation. The facts are presented after objective analysis.
If an analyst analyzes a video and is able to confirm though reconstruction and restoration that an object or person has a number of atributes then those atributes are facts.

However, an analysts most important skill is the ability to identify features that are not reliable or that contrast, rather than compare with a known object or person.

I am sure that Reuben could have said a lot more (I imagine there was a lot edited), but the report has highlighted the scary fact that there are people in the UK and around the world presenting this sort of stuff and they are full of unreliable images caused by a lack of understanding and questionable terms to baffle a jury.

The more times that things like this get shouted about, the better it will be for Forensic Video Analysis and the legal system.


App Reviews – Clock Check and iCrimeFighter

These two iOS apps fit nicely together so I thought that joining the reviews would help more. (If you are an Android user and know of similar apps then please let me know or, if you have done a review, send me the link and I will include it here).

The first one, Clock Check, is “an application designed to aid CCTV engineers and Law Enforcement personnel when calculating the time discrepancies on CCTV systems.” Firstly, it does what it says it does, and with no fuss. It also has a few little extras that make it a little more than a basic time calculator.


It has the ability to sync with your devices time. This is great if you have your iDevice set to sync time automatically. The problem though is that the time shown within the app doesn’t move. Its static. I think a great update would enable you to see the realtime moving along and then after setting the system time hit the save button. The times would then be saved.

As it is now, having the ability to sync to realtime is good but you still need to change this slightly.

Time checks can be saved with a user generated title and the app also saves a number of recent checks.


The other good function is the ability to enter in the time of an event and then for the app to show you what time that would be on a DVR.


The app definitely helps the mathematically challenged like me! Its a good start but needs a few refinements to be a great tool in the box. The first one, as stated earlier would be the ability have your system clock shown within the app so you would not have to change the real time at all.

The second would be the ability to export the saved checks, perhaps to a dropbox or email address as a pdf. These would then be added into your case records.

So, it it worth £1.49? Well that’s up to you. On its own you may not think so but if you included it with another app then your opinion may change.

This next app, iCrimeFighter, is an “investigative/evidence gathering application! Use your iOS device to collect all the information you need at the crime scene or event. With iCrime Fighter you can capture photographs, record videos, record interviews, and write field notes.”

This is a free app so offsets the money spent on Clock Check. You can add job details and then see these on a map.

Starting Interface

Starting Interface

IMG_0593Once the ‘job’ is entered into the database, you have the ability to add items to it.

IMG_0594This is where you could add screenshots from Clock Check, photographs of the Camera locations and camera views, notes on the scene etc. You can then email them all to yourself as one job.

Both apps together make a good package for Digital Multimedia Evidence Retrieval.

Lastly, and just to close this up, you may need to log other reference number’s or even design your own purpose built database. Take a look at Bento for Ipad. Although this is currently at £6.99, if you need something to keep track and link various reference numbers specific to your role then this is a very good tool to use.

Forevid and x264vfw

Forevid, using the words taken directly from its home page, “is the world’s first free, open-source software for the forensic analysis of surveillance videos”.

My own take on the software is that it is an enhanced viewing and logging platform, for use during the visual analysis of surveillance videos. It does not communicate with proprietary or unwrapped video streams but does deal very well with transcoded or standard AVC streams.

The Forevid site has some very good tutorials and guides, so I wont duplicate what they have already done. However, it is worth highlighting a few points.

Once installed on a working system, the Program folder can be copied and placed onto a system that has reduced user rights. If a computer user is unable to install software then this is a useful workaround.

There are many systems now that export basic AVC streams. Each stream comes as a separate file. They can either be played direct using ffmpeg or rewrapped. Forevid is a really handy program to load all the video streams and then go through each one.

If the video needing to be viewed and collated does not allow for import into Forevid but you are able to transcode (For viewing purposes only), it just has to be in a format that ffmpeg can decode. I have been having some very good visual results using the x264vfw codec.

x264vfw Configuartion

x264vfw Configuration

These files drop and play in Forevid with no problems.

The best way to learn the program is to download, install, and then run it through with a few test scenarios.

I am finding it most useful when dealing with multiple and lengthy video files that need to be viewed and logged.

Two reports can be created at the end of that specific video investigation.

  1. Video summary, detailing what videos were used and whether filters were applied to them (handy for when you apply a 720 x 576 resize when importing 720 x 288 AVC streams.
  2. Bookmarks, detailing every image and it associated information. It works with frame numbers so is great when your original video is also frame based.

A couple of examples can be found here:



It definitely has its place within your video toolbox.