You can now get battery-powered surveillance-cameras with a SD memory-card...discreet and powerful! download the card about once a week, i believe.-play through a TV, Computer or even some printers.
They are called Game Cameras, originally designed for watching animals in an area day and night (Search Youtube and Google and you can see just how good they are). We leave them out in the bush for weeks on end, getting rained on, frozen and they continue to work.
The big benefit of them is that they don't use up a lot of battery life just sitting there doing nothing and really only use power (battery life) when something triggers them to take a series of photos or a video. Combine that with the superb, very low discharge Eneloop Rechargeable Batteries and they can go months.
I am surprised more airfields don't have them in hangars etc, a very small price to pay to get a photo.
In case any of you do look at them in the future, the one's to get are those that can take IR photos and video WITHOUT showing any sort of red light on the front (dead give away in a dark building).
Hope that helps.