Say for arguments sake i Design a T shirt(i will use a t shirt as and example) with some pattern or image i copyright, And then some person starts selling a blatant knock off of my shirt.

How would you enforce this, As anyone can make a T shit, but they have infringed my copyright once they make a copy of my printed design/pattern/logo.

How would you enforce this, what would you serve on someone to make them stop?