Measure the height and width of the lattice panel.
Cut two pieces of 2-by-2-inch board 1/2 inch shorter than the width of the lattice panel and two pieces of 2-by-2-inch board 3 inches longer than the length of the lattice panel.
Set the guide rail of the router to remove 1/4 inch of the 2-by-2-inch board. Set the depth of the router to 3/4 inch. Route the long edge of both the long pieces of 2-by-2-inch board creating a 1/4-inch shelf to set the lattice panel on. Start routing 1 1/2 inches from the end of the board and stop routing 1 1/2 inches from the other end of the board. Leaving the ends intact will allow you to screw the framework together easier.
Place the pieces of 2-by-2-inch boards around the lattice panel, framing it. Align the ends of the framing pieces, creating a rectangle around the lattice panel. Put the shelf you routed on the bottom on the inside of the frame. Insert a screw through the side of the long boards into the ends of the short pieces.
Insert 1/2-inch finishing nails through the lattice panel into the frame every 1 foot.