Place the photograph between two pieces of tissue paper. Do not bend the photo as it may crack and break the delicate corners into pieces. Use extreme care.
Use a steam iron on a low setting and gently press down on the top layer of the tissue. Work back and forth slowly and with a light-handed touch to smooth the photo.
Remove the photo carefully from the tissue paper and place it between two paper towels. Place a heavy book on top of the covered photo while it dries and begins to flatten. This process is for older more fragile photographs. Use caution when working with these so as not to damage the pictures any further.
Flatten a newer photograph by placing it in a large envelope and sending it through a laser printer twice, once in each direction. Newer photographs usually have less damage, and are easier to flatten without causing any further damage. The heat from the laser printer helps to moisturize and smooth the photo. Place the photo inside of a scanner bed or underneath a heavy book for a day or two.