In the "Copyright Act". Please don't ask me for specific quote, because I don't know US law, but from what I've read on the topic (http://www.ucop.edu/ott/facu

In the "Copyright Act". Please don't ask me for specific quote, because I don't know US law, but from what I've read on the topic (http://www.ucop.edu/ott/faculty/crothers.html http://www.ucop.edu/ott/faculty/crothers.html, http://www.wisconsin.edu/gc-off/deskbook/copyrgt.htm http://www.wisconsin.edu/gc-off/deskbook/copyrgt.htm), it's pretty much the same as in the rest of the world, that is: Copyright is automatically granted to the creator of the work (or his employer, in case of "work for hire") and anyone who wants to legally use it needs permission (license) from the copyright holder.