Photographs are important pieces of our history and they are also fragile paper documents that can deteriorate rapidly if not cared for properly.  In the first stage of  your unit or activity,  introduce students to the proper handling and preservation of photographs. Always include lessons in basic conservation when using photographs (or any other historic objects/artifacts/materials) in your teaching.  The following sites offer especially good information:
The American Institute for Conservation of Historic and Artistic Works
The Northeast Document Conservation Center

• Wash hands before handling photographs; handle by the edges. Be especially careful with negatives because a finger print will make a negative unusable. When photographs or negatives must be handled, protect them with polyester sleeves or bags.
  
• Avoid plastic lamination. This process will destroy the photograph. You might, however, laminate a copy or photocopies for classroom use.
  
• Never use scotch tape, glue, thumbtacks, paper clips, or rubber bands to fasten or secure photographs. Use photo corners which do not permanently fasten photographs to a backing.
  
• If possible, always use acid-free folders or envelopes for storing photographs. Check with your local office supply store for acid-free 100% cotton materials .
  
• Do not use self-adhesive albums.
  
• Do not store photographs in attics or basements or rooms where the temperature may become extremely hot or cold or where moisture is a problem. Store in an area that has a relatively constant temperature.
  
• Do not display photographs in direct sunlight or under direct fluorescent lights. Always use acid-free matting board to protect the photograph from harmful materials in frames (especially wooden ones) and glass (especially Plexiglas, which may loosen the image from the photograph).
  
• Label photographs as to who, what, when, and where. Write with a soft-lead pencil only in the margin of the reverse side. Better yet, write all the information known about the photograph on acid-free paper and enclose that with the photograph in an acid-free envelope or acetate sleeve.
  
• Black and White photographs have much longer life than color images.  Use black and white film for important documentary photographs such as family portrait, reunions, and special occasions.