You could charge $10 per foot image or $100. The success of your feet images is contingent on the amount your target viewers are ready to spend. You could consider offering a reasonable monthly fee, for example, $29 per month to get access to a handful of your exclusive foot pictures every 30 days, if you are using a subscription-based system. If you would like to charge additional fees for more pictures you can do that by logging into your account. You may have to experiment with different price points to discover what is most effective for you.