AutoScreenShot is a portable free tool which can save an image of your screen at regular intervals, perhaps useful if you need to monitor what others are doing on your PC.
Launch the program and it presents a few simple options. You can choose the time between each shot, for instance (two minutes by default). You're able to decide the maximum number of images the program will retain - just the last 200, say - so that it won't fill your hard drive. And AutoScreenShot can also recognise duplicates, which means it doesn't have to save images if nothing has changed.
With everything set up, launch the program and it'll go into action, just saving grabs at whatever interval you've defined. And if you copy AutoScreenShot into your startup folder then you'll have a simple user monitoring system.
We say "simple" because it's not exactly difficult to bypass. If anyone checks your startup programs, or Task Manager, they'll find the program, and browsing your screenshot folder will reveal exactly what it's doing.
Still, if you just want to monitor novice or non-technical users, or perhaps you'd like the screengrabs for some other reason (creating documentation, say), then AutoScreenShot could be useful. Give it a try.