One way to mount a stretched canvas on a wall

 

Staple a side of a milk carton to the back of the canvas frame as shown in the photo.

The stapled carton.

Do the same to the oppersite side if it is a small canvas as shown here.

If it is a large canvas you can put cartons on all four sides and also more than one on each side if needed.

Mount the canvas on the wall as shown

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