The reliability of the various algorithms (Gaussian Face is one of many that can be used) depends on a great deal of parameters, primarily orientation of the face (profile is fucking hard), lighting conditions and the size of the set you're trying to verify against. The first two ought to be very good for mugshots, the last...not at all. When trying to tell if your mugshot is one of millions of others is going to be very difficult.

If you're comparing an image from CCTV against mugshots its not going to work reliably at all. Not even close. The pose, lighting will be all wrong.

Mugshots are also not designed to be plugged in these systems, when you want a really good set of faces to compare against you take multiple photos of the same subject in a variety of poses and lighting conditions and construct your model from all of that data, not a single photo.

You certainly will not hit anything like 100% - it will beat humans at it (for a start humans can't verify against a set anywhere near as large). Frankly I've never been involved in any projects looking at sets close to that order of magnitude but I'd be amazed if it was >95%.

I'd expect the results from the program to actually be a list of faces it thinks are most similar in descending order of probability, which will then need a human operator to look at and then decide. But this is still imperfect.

If I give you two photos of people you've never before who look extremely similar and ask you if they're the same person or not and you're going to struggle. If they're from CCTV you've got no chance.

Claiming its 100% is disingenuous to the extreme. The leading private sector sources for this software don't claim that (think the best I've seen is ~97%) and that's on smaller more controlled data set.

I also don't believe the police would even attempt to plug this into CCTV. It just won't work at all.