At first I thought this might be a bit of a fools errand - large areas to cover, false alarms from wildlife etc. (I've done a lot of this sort of thing for site security) Then I thought some more.
Specific areas may have choke points where people may gain access. If so...
Stills: There are a LOT of "Wildlife cameras" that are fully self contained. Run off batteries, take a shot (usually with white light, which means it stands a good chance of being stolen itself if it alerts the thief), store on SDcard. Probably not good unless it can take a covert shot, and you don't need instant alerts.
However - photos taken by night, even with IR floods, are rubbish at distinguishing facial features (even numberplates are tricky) - without some quite seriously expensive kit. Even if the camera isn't stolen, what it produces may be no use beyond "Yes, there's a person, maybe"
Any camera that triggers on PIR movement would do, or a regular movement with motion detection somewhere. The problem with offsite modect (Zoneminder!) is that you need a reasonable framerate to ensure your guy doesn't slip through between images. Say 2-3 fps on a narrow area, maybe 1fps if there's a bigger area to track - but then that means a smaller person on the image, and more chance of missing something, or having it detected as noise. Zoneminder will run on an rpi - there's even a useable image - but it is cpu bound at low fps.Might still do it though. Naturally you'd need decent 3g or by some miracle, wifi but you'll probably be changing batteries every day.
Realistically, if you intend to do this to any degree of reliability, you will need (IMO only!)
Covert:
Fixed IR cameras fed by poe over cat5. These could be recorded/monitored locally via a server, or remotely over tinternet. (Beware volunteers falling asleep - I imagine we're talking 3am type visits) These will not provide useful images, but may help notify someone's there beyond a traditional buzzer PIR sensor which could alert on deer or foxes or birds.You will need IR flash lighting (if they exist?) or IR floodlights (these definitely do).
Overt:
White light PIR lighting, white light cameras. These are very reliable in recording events with zoneminder since there's a very obvious trigger moment when the standalone PIR turns on. Similar network to above.
All this could be done at the cost of a few hundred, perhaps a couple of grand, for a small area, using consumer grade kit. If you want it to last , then increase that a lot.
All these mean you may get a blurry picture in black and white of something moving at a certain time. I doubt hugely whether it could ever be used to identify a person, let alone in a court of law, even if the court accepted the image as evidence.
Some more thoughts:
Will the bad guys have night vision? If so, IR floods will be very obvious! If not, are they using white light and be easily spotted with non-IR cams?
Even IR floods show some white light and can be spotted in darkness.
I imagine bad guys
certainly recce such places in daylight and would spot many cameras and
lights. Also exits, places to park.
So, lots of thinking and writing later... I still think this is a fool's errand, sorry!
If it's a real problem (I have no idea), and if it's common enough to warrant volunteers watching CCTV streams all night, why couldn't they sit out in the woods too? They will notice far more being immersed in the surroundings than you could EVER hope to remotely; they won't suffer dropouts, failures or distractions; they're instantly on the spot and can alert the police without first having to verify what they're seeing; Take car number plates; Move around from place to place, etc etc. (Beware of stumbling on doggers, ofc!)
If it's a real and very rare/occasional problem, then frankly I can't see what can realistically be done against it. The odds are definitely in their favour.
