Use hinges or corners made of acid free paper or mylar. Paste should be chemically intert. Methyl cellulose, rice starch paste, and wheat starch paste are acceptable pastes. Never use rubber cement or pressure sensitive tape. Aluminum frames are safe, light-weight, relatively inexpensive, and came in all sizes and colors.
Wood frames can attract insects, and they give off gases that are harmful to the photograph.
The long-term safety of plastic frames has not been established. There are many types of plastic, some are safe, some are not. Display photographs in the lowest light level practical. Display photographs in tungsten light only. Sunlight and fluorescent light contain ultraviolet rays that will fade or discolor photographs.