I have never done it on purpose, so it probably would become contrary and not work, but when I have copy/pasted a file from one partition to another, it seems to redate the files to that date and time. Of course, if you wanted some other date/time, that wouldn't help at all.
EDIT: Another way that you might be able to do it, if it is a text file. Open it in an editor and then save it. Again, this will just redate the file to the current time/date. This might work for other file types, if they can be opened in some kind of editor, but I haven't tested it.
EDIT: I failed to note that your question was about image files. I just repeated the same process opening, then saving with Irfanview and it had the same result.