To answer your sub-question: To see the date the file was created, add
-U (OS X and other BSDs) or
-c (Linux) to your
If you were on a Mac and use Time Machine, or if you were using an app that makes use of autosave in OS X 10.7 Lion and later, use Time Machine to check for previous revisions of the file, and then check their metadata using a tool that understands the metadata of that file format.
Depending on what OS you're on, there may be other pieces of metadata (extended attributes, etc.) for the file embedded in the filesystem's entry for that file, not in the file itself. So the answer would vary by OS.
It's always good to specify which OS(es) and OS versions you're talking about when asking questions here. Gimp runs lots of places including OS X and Windows, so we can't assume you meant a certain flavor of Linux just because you said you used Gimp.