At the moment the photo limit is 640 by 640, which is a little annoying IMO. It is practically impossible to use anything found off of Google images. I suggest a slightly large limit, maybe 750x750.
Here is a reference image that is 750 by 750
http://www.landchoices.org/media/images ... 50x750.jpg
This shouldn't break the formatting too much, if it does, spoiler tags could be used for larger pictures.