I think you should re-think your business model.

People who join "membership" sites expect to see thousands of images - not 12. Even if you clearly state what you have before they join, nobody reads it. If they do understand you only have 12 images, they won't join. You'll find a LOT of refunds and chargebacks. If you exceed your chargeback limit, you're out of business.

ccBill has a side business called DRM Networks. Check that out. You can charge per image and it's encoded so it's more difficult to copy the image.

Before thinking about billing issues, what are your plans for preventing un-authorized use of your images? Its sad, but Titan Media probably spends more on pursueing copyright violations than they do on promotion.