These are cloth napkins purchased from Crate & Barrel stretched over a frame. I purchased stretcher-bars to make the frame (the same kind used by artists to stretch canvas, so they are made for the purpose of attaching fabric). I purchased them from www.frenchcanvas.com. These are put together with a rubber mallet (no hardware required). I used a staple gun to attach the fabric. Just be careful with the corners. Neat corners will make or break the final look of these types of projects.
See ABSTRACT BIRCH FOREST and POTATOE SACK WALL ART for similar projects.