This question has been asked so many times that it can't be kept track of anymore.
The answer to this extrememly frequent question is:
The same applies to pictures. You can't protect your pictures on the net either, b/c you can do various things to get them too: drag the pictures into the address bar, get them from the cache, print screen, snapshot (Mac), etc.
If you don't want anyone getting your source code or your pictures, then don't publish them to the web.