As BTCforJoe said, you can't make the entire banner an image. Basically, if images are used for positioning or general text styling -- which CSS should be able to do --, then it's not allowed. But usually I allow little logos and such which can't be properly replicated in CSS.
Can you consider, as an exception, our request for an ICO project?
https://okoin.ioSorry, no.
Auction ended, final result:
Slots BTC/Slot Person
4 0.14 ChipMixer
2 0.12 Blocklancer
3 0.10 Aengus