Ahh, I didn't realize. Sorry about that. I thought that PNG would give better quality, but if you can't download them they're no use lol... I'll try to upload my images in JPEG format from now on
As for the size, I like to keep them very large because then people can have more to work with and can always resize them to what they need them to be after editing.
Thanks for the comment and bringing that to my attention!