Original image

step 1 of 4

step 2 of 4

step 3 of 4
you can either- erase the bread to fit the knife, or ctrl -click and invert then delete the selection. you should have the outline of the knife

step 4 of 4
http://www.pxleyes.com/
find one of the seeds that looks like a nail or a screw
You the burn tool to get a rusty look

Final result

