Choose a printed or painted fabric to display on the lightbox. Measure the size of the lightbox frame you need. Ensure that the fabric is 4 to 6 inches longer and wider than the frame because the fabric must stretch over the 2- to 4-inch-deep sides of the frame.
Lay the fabric on a flat surface such as a table. Pull the fabric taut so it is completely smooth.
Lay the lightbox frame face-down and centered on top of the fabric. Fold the right side of the fabric over the side of the frame and onto the back.
Attach the folded right side of the fabric to the lightbox frame using the canvas tape. Pull the opposite side of the fabric so it is stretched taught across the front of the lightbox. Attach it securely to the frame. Continue with the top and bottom of the fabric so all four sides are affixed to the lightbox frame.