Eccentric picture 'hooks'

I live in the topmost floor, I have almost no horizontal wall to mount pictures.

I needed to mount some pictures to a slanted wall.

This piece engages with the inner groove of my pictures and prevents them falling down.

Each picture requires four of these (two to hold the top of the picture and two to hold the bottom)

It's made eccentric, so it's possible to correct minor mistakes committed to the placement of the hook.