Tell GIMP to grab a screenshot of the entire screen after a delay, and
then immediately after you activate the screenshot, before the delay
expires, lock the screen so the screensaver kicks in. I tested this and
it works on Linux; I don't know if it will work on Windows.
Another option would be to run the Grid inside a VM, and take a
screenshot of the VM window.
Aside from the issue of taking a screen shot of a screen saver, note
that putting library computers on the World Community Grid will increase
their electricity bills:
I hope you will make sure that the people to whom you make this proposal
are aware of this fact. Given this fact, it is unlikely that they will
be willing to join their computers to the Grid, but this is just why it
would be disingenuous not to make them aware of it.
gimp-user-list mailing list