Many of my coins images are saved as .png's, but Numista seems to only accept .jpg's. A short snippet of code should fix this, and allow multiple image types to be uploaded.
http://www.facebook.com/NumismaticsUK
I'm not an expert in any kind of coins, but I reckon I'm good at research and will do my best to help. Feel free to tell me my identifications/valuations/gradings are wrong. It's the only way I'll learn.