Take 4 canvases of each size), paint them a solid base color and add vinyl or stenciled design. stick decals onto canvases, paint the whole thing and then remove the stickers to reveal the wonderful artwork!
I love this photo wall--the square layout is fantastic and a nice balance of color black white photos. Do you prefer color or black and white or a mix in your wall galleries? I have either all color or all blackwhite in my house.