App for automatic screenshots on a timer with on/off switch?

As someone who never remembers to take screenshots, I was thinking that having an app that takes screenshots at intervals would be helpful. I've looked around a bit today, and have found apps that do such things, but a lot of them require that to be the ONLY state -- meaning there's no hotkey to start or stop the interval timer.

Does anyone know of any apps that would work with a fullscreen game that won't trigger hacking warnings?