Fill a large pot with water and bring the pot to a boil. Remove the paper frame of the artwork by gently pulling off the back board. If this is taped in place, place oven mitts on your hands and hold the taped section over the steam coming from the pot. This should loosen the tape and allow you to peel it off gently.
Remove the picture and place it about 1-1/2 to 2 feet above the steaming pot. Hold the top and bottom edges of the artwork snugly and pull just a tiny bit with your hands as you move the picture over the steam. Do this until all the wrinkles have been removed.
Immediately place the damp picture onto a hard, flat smooth surface that is larger than the picture itself. Sheets of Masonite or scrap linoleum are excellent for this. Place another similar surface on top of the picture. Clamp each corner of the material firmly shut and place a heavy book on top of the boards. Leave this overnight.
Unscrew the clamps and remove the heavy book. Very slowly remove the board. Use a piece of cardstock to lift the art up almost like you are flipping a pancake with a spatula. Place the art back into the frame. Secure the paper back board to the back of the frame with masking tape. Wipe the surface of the boards you used for pressing with a paper towel to make sure they are dry. Place the entire picture, frame and all, into the boards and set the heavy book back on top of it for another full day.