http://www.gmdsoft.de/menne/z3c/animget.htm
Animget was originally intended to make ripping sprites from emulators easier, but it works with just about any program (some better than others).
It checks every 10 milliseconds to see if the screen has changed, and if it has it takes a snapshot. It's free and a very small download, so maybe someone will find a use for it.
(hopefully not just for mario/megaman/zelda clones... )