Take a photograph of the stuck image or scan it as a backup. If the photo cannot be released from the frame without serious damage, the duplicate backup image can possibly be enhanced by a photo lab.
Place the photo and glass into a shallow container, image side up. Fill it with enough distilled water to cover the items.
Let the photo sit in the water for at least 20 to 30 minutes. Monitor it from time to time to see if the photo is floating free of the glass.
Place the photo and glass on dry towels and blot away excess water. Gently insert a thin spatula between the photo and the glass. Peel them apart very slowly.
Flatten the photo on a dry towel or paper towels and weigh down its edges with paperweights to prevent curling. Allow the photo to air dry.