The answer adhesive hooks
Ranging from tiny cute one to big ones.
If you plan to hang a framed work I suggest you go for the big ones.
And do check the weight capacity. Some of these have it described on the back.
I also read that there quite easy to remove. Just add oil or water I think. Never tried it though.
Will let you know when I get the chance to.
I think these are fun at holding up matted works like these :)
Two on the bottom.
One on top :)