Modern technology can be especially useful in a situation involving photos stuck on a piece of glass. A photo print can be photocopied, scanned, or copied using a drugstore enlargement machine--glass and all. So, before you attempt to remove the photo, and, especially if you do not have a negative or other means of replacing it, make a copy and set it aside. Once this is done, you can attempt several methods to remove the photo from the glass. However, these methods only work in some cases, not all, so make sure you have scanned your photo.
Methods for Unsticking
Use a standard hair dryer to heat the glass from the back evenly, slowly working over the area of the photograph. While maintaining the heat, gently pull up a corner of the photo. If it lifts easily, continue to remove it, using heat as necessary, until you have lifted the entire photo from the glass. If you have only been able to remove a portion (carefully and without tearing it), or the photo does not lift easily away from the glass, try the next method.
Place the photo inside a large plastic bag, leaving the seal open, and lay it flat inside the freezer for 24 hours. Use protective gloves when handling glass to avoid injury from sharp edges. Carefully remove the bag from the freezer and gently peel the corner of the photo away from the glass. If the photo lifts easily, continue until the photo is entirely free from the glass. If all (or a portion) of the photo does not loosen easily, try the next method.
Lay the photo and glass on the bottom of a shallow pan and add cold water to the pan until the photo and glass are well covered. Place the pan, lying flat, in your freezer for about 10 minutes. Remove the pan from the freezer. Carefully lift the glass out of the pan and lift the corner of the photo away from the glass. Continue lifting until the photo is completely removed. Dry the photo by placing it on archival paper inside a large, heavy book. Let dry for two to four days.
To avoid damage to your photographs, frame using a mat or thin strips of felt on all sides of the photo, between the photo and the glass. When using the second freezer method, be careful not to freeze the water. If you don't have archival paper, you can use wax paper to dry your photographs.
Please note that these instructions are for photograph prints only. They are not intended for use with a printer copy of a photo. Always wear protective gloves when handling glass to avoid cuts from sharp edges.