I have been doing research for a friend of mine that wants to sell her stamps online, and I came across lots of information regarding the usage of rubber stamps and selling your creations.
Angel Companies are companies that will allow you to use their images to be used for handmade art, cards, etc in local resale venues such as art and craft shows, etc. However no mechanical reproductions are allowed.
PLEASE do your research in regards to the stamps you are using, before selling your wares - I would hate for the everyday Craft Momma to get sued. Here are some articles with lists of the companies that are affected: