Rubber is used to print images on a surface. Rubber stamps can be made out of an image with the principle of vulcanizing rubber.
In the art-world there is also the rubber stamp art. See also mail art. Sometimes the rubber stamps are self-made or even carved out of erasers.
Rubber stamp is also a political adjective, referring to an institution that has little power and rarely disagrees with more powerful organs. For example, in a dictatorship, the parliament may be little more than a "rubber stamp" of approval on the dictator's decrees. Conversely, in a constitutional monarchy, the monarch is typically a rubber stamp to an elected parliament, even if he or she legally possesses considerable reserve powers.