You know what I think is the most effective way?
If you download an image, why don't you just leave a gallery comment for the image you downloaded? If you think
it's nice, say so, and why. If you think that the quality of the image is not so good, you can also leave a comment
saying that and how you think it could be changed to be better. If the image is really bad and violates the Minitokyo Policy in one way or another, hit the report button and explain
why.
I find it interesting that most members would suggest posting in the forums when leaving a gallery comment behind for
the image you downloaded is the first thing I'd do.
If you do that (without spamming of course - give the comment a little bit of thought), there's no reason why you
should be in need of credits for downloading :)