I was wondering if a histogram of the image could be used to determine much.. Looking at the bottom screenshots I do notice that there is a tendency to have very unsaturated colors, possibly use a very limited color palette, and contain relatively few image features of note.
Though you should be careful about accidentally excluding cool concept art. (Though not technically 'screenshots', I certainly wouldn't (corrected by a edit) mind if people slipped some concept art into #screenshotsaturday, if still gamedev related)
Edited by Servant of the Lord, 21 January 2013 - 04:30 PM.