U.S. Patent No. 6,022,219 (.pdf)
Is it a bird? Is it a plane? Is it a Pollock? No, it's the result of using an "infant's posterior" as a rubber stamp. Thanks to the inventive kit disclosed herein, you can now make a "remembrance that results in a fine art end product which is not easily recognized as merely a remembrance." If keeping track of your child's height, or making a clay mold of their footprints is too cliché, then use your baby's ass as a rubber stamp to make something that nobody will ever recognize as representing your kid! The instructions are quite detailed, enumerating everything from what paints work best, how old your infant can be, and even how to hold your infant with attention to whether or not they have neck strength. Follow the steps and voilá! You've got yourself a masterpiece. And an infant's posterior to clean up.