This image was accepted at Dreamstime, Fotolia and iStock, but DepositPhoto rejected it for poor lighting:

http://www.dreamstime.com/royalty-free-stock-photo-valentine-image12737615

It's a 3D render.  I couldn't find any way to ask them for clarification, so I thought I'd ask here for suggestions.

You always can resubmit it and add your comment to reviewer.
I think that will help. Also if it is 3D render then you can add that to your description... As well you might think about making one better lighened scene render as additional version...

Good Luck!