Photos should be a maximum size though.It would be a shame to lose some part of the cool pictures because they are too big.
I think we did have a maximum size requirement on the old contest, which of course made sense for the reason you stated. But long lists of rules put people off, even if most of them are common sense. It's better to just leave that up to the person posting it to decide what size shows their pic to the best advantage. This reminded me I needed to resize mine though!