Place a sheet of brown kraft paper on your cutting surface.
Place the frame right-side up on the kraft paper.
Hold the frame firmly in place and use a box cutter to cut around the edges of the frame. The frame will act as your template so that you have a good fit.
Apply a thin line of white glue to the edge of your frame on the back side. If your frame molding is flat, the glue should be applied to the very outer edge. If the molding is angled, apply the glue to the flat edge that is just outside the opening where the artwork lays.
Lay the kraft paper on top of the glue, lining up the edges of the paper to the frame edges. Smooth the paper. It should be a perfect fit. If there is any overhang, trim it off after the glue dries. Drying will take about half an hour. Once the cover is attached, your frame will be ready to be wired for hanging.