Can you believe this? I never thought of raw edge reverse applique! This is from The Long Thread blog by Ellen Luckett Baker. She suggests that if you're going to put this pillow or quilt to use, that you should machine stitch around the circles too, of course.
Note for new quilters: Reverse applique is when you cut an opening in your fabric in the shape that you want (like circles in this example), then place the printed fabrics underneath. Normally you'd turn the raw edge under and hand sew the opening.