There are a few spyware/surveillance-type apps out there that are designed to run "stealth" and also perform functions like keylogging, web-blocking, etc. Generally these are geared for parents who want to spy on their kids or corporate office scenarios. Most of them are quite expensive ($60-90) and bloated.
What I am looking for is
NOT a program for spying. (Well unless you consider it spying on myself!

) I do some database development as well as some lightweight PHP/javascript work for various customers and have found it quite difficult to accurately log my time for billing purposes. Part of this is my fault in that I am very bad at remembering to take proper notes after a development session. Usually I just do the work and then pray that I will remember what I did several weeks later (I know-- terrible!!

)
Anyway here's the request: a very tiny and efficient program that just takes a snapshot of my desktop and saves it to a specified folder (with the filename set to the date/time of the snapshot) at set intervals. The interval and folder should be selectable. Ideally the format for the images should be PNG since it is very high quality and would give the most accurate rendition of the desktop. But I guess GIF or JPG would be OK too.
The thread should run at Low or Idle priority so as not to interfere with the work being done in the foreground. I don't know how possible it is but the main thing I would be concerned about is a noticable pause while the app is doing its thing. Whatever could be done to minimize this effect would be obviously the best.
This way, when I am ready to review my invoicing, I can go back and review the screenshots to help me remember what I was working on 2, 3, 4 weeks ago etc.
I think this would be soooo useful and I would appreciate any comments or feedback on it!