Don’t buy either, and ignore the string. For little things that are not too breakable and assuming at least two weeks since painting, 3M Command Strips are amazing.

I typically use 3 per picture, to keep sides and top against the wall. Just adhere them to the back of the frame and literally place the picture where ever you like. Done. If you ever need to take them down, it’s just Velcro, and the sticky tape is a command strip the cones cleanly off the wall