US8061611: A patent held by Anoto describing how to recognize OID patterns and how to determine if they are in the right orientation
US6548768: A patent held by Anoto describing how to use OID to determine x and y coordinates on a page
DE202013000802U1: A patent held by Schleich describing OID animals similar to the ones by Ravensburger. The only difference is that Schleich does not need a flat surface on the animal to print the OID on. So far no such animals have been seen in the wild.