Screen Capture freeware recommendations?

[Dan <dan27649@xxxxxxxxx>]

I am asking for recommendations on Screen Capture freeware.  I am
pretty sure I have, in the forgotten past, found one or more freeware
options that have these features:
* Ability to pre-define area to capture
* Automatically save image to pre-defined filename and format
(including .PNG format)
* Maybe more

Also, it would be nice if it had an option to "reverse image" the
image so that the green-screen black backgrounds would be converted to
white.  This is not a biggie, though, as I can always start another
session with a white background.

TIA, 
Dan