From A to O - a lot of
"thou must" - but who can stop the determined?
In this world in which we live, there is only one way to prevent work being copied/manipulated, and that is to not post it - in an electronic format [ in which case you've defeated yourself ]. Even work in print is copied; even if only to provide an electronic version to read
Even artwork with copyright symbols across them are successfully pinched (go read many DeviantArt posts).