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I've been asked to recommend an IP-based security camera in attempt to prevent, or at least record, repeated acts of vandalism occurring at the front of a property.

Budget is a concern (The damage is minimal but frustrating) and there are plenty of cheap home/soho models around that offer all the useful connectivity functions for a reasonable price. The one thing that conerns me is that the low capture resolution, coupled with what are likely to be poor quality optics won't be enough to be able to identify the subject from much more than a few metres.

Assuming decent lighting and that we get a front-on still of the subject, what would you consider to be the useful range of a 640x400 camera for producing something that the police might reasonably accept as proof of someone's identity?

SmallClanger
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This is more of a legal question than a technical one, so before I answer I'll provide the usual disclaimer: IANAL.

From my (unfortunately rather extensive) experience with this, the police usually already have a good idea of who's responsible. They just have to prove it. Unfortunately, criminals these days are smart enough to wear scarves or bandanas over their face, so that only their eyes are visible to CCTV. This makes identification difficult, if not impossible. You've just got to hope that you've got a dumb one! In such a case, even a low-res blurry image of someone's face can be enough evidence to issue a warrant to search their premises, to find further evidence of graffiti or damage. It generally depends whether they can convince a judge (or the CPS, in the UK) that what they have constitutes reasonable evidence.

If you're dealing with spray-paint graffiti, they can ship paint samples off to a lab and have them matched by mass spec / IR spec. This actually resulted in a conviction in a particular case I know of, where they ended up matching the tag to a string of other graffiti incidents. The guy ended up with a hefty fine and a long suspended sentence.

However, from a technical standpoint, you're not really looking for higher resolution; you're looking for better quality pictures. Sadly, the camera industry has been pushing "MOAR MEGAPIXELZ!" as the standard for better quality, but it's simply not the case. What you're looking for is a camera with a good quality lens, decent nighttime performance, reasonable framerate, and low chromatic abberation. I'm not a photographer, so I can't really give you advice on what specs to look for, but the hard truth is that quality costs money.

My suggestion would be to go for something with a decent framerate, over something with a larger image size. See if you can arrange a demonstration with a salesperson to see what the image quality looks like, and decide for yourself whether you consider it clear enough to produce a quality picture. Also keep in mind that there's nothing to stop the vandals from attacking your camera, so don't blow a load of money on it and be surprised when it gets stolen / smashed.

Finally - get a motion-sensor light (PIR). They're cheap, easy to replace, and make vandals stick out like a sore thumb at night.

Rory Alsop
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Polynomial
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    Add low electronic noise to that, compare low and high resolution photos from different cameras with the lens cap on. The more pixels packed together the more neighbouring pixels they interfere with electronically. Higher resolutions can decrease the quality overall. – ewanm89 Aug 04 '12 at 15:42
  • @ewanm89 Yeah. Also, verify that the power supply you're testing with is exactly the one that you'll be buying with the device. I've seen great results on a demo, and then found out that the real PSU shipped with the device is an awful full-wave rectified supply with no decoupling, causing horrible noise on the image. I ended up building my own supply for it. – Polynomial Aug 04 '12 at 15:55
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    @Polynomial Added a Wiki link to your answer, to define IANAL. 'Cause I'm sure some Joe out there is going to not know what it, is and think you're talking about your personal enjoyment of rectal intercourse. – Iszi Aug 04 '12 at 16:20
  • Haha, I lol'd. Yeah, that acronym doesn't come without certain presuppositions. – Polynomial Aug 04 '12 at 16:21
  • Thanks, all. I hasn't considered electrical noise as a factor; I'll add that to my list and point taken on the frame rate. It's only been a few incidents so far, so I'm hoping it's dumb opportunism and we'll get them in the clear. (@Iszi Acronym understood. I also ANAL...) – SmallClanger Aug 04 '12 at 17:24
  • Oh, dear. It seems I may have turned this into The Comms Room now. – Iszi Aug 04 '12 at 18:36