Photographic materials are unstable and frail but their life can be extended if you understand and remove the conditions that can damage them. 

The nature of these materials consists of at least two layers: the emulsion layer (particles and dyes) and the "support layer" (paper, plastic, etc.). 

Temperature, humidity, light, pollution and contaminants can deteriorate them. You have to avoid the contact of photographic materials with these damaging factors. 

The photos needs to be framed properly, stored in plastic envelopes and cleaned using a soft brush. You can also reproduce them and retouch them. It is a good idea to scan photographic prints and transfer film to dvd to provide a digital copy that can be stored away from the originals in case of fire, flood or other disaster.

Very old photos can be digitized and restored with tools such as histogram for restoring contrast and the Clone Tool that fixes damages. After you scan it, you can use Black & White Points. Often it's easier to repair stains in color mode. Clip the tail of pixels off and experiment with contrast to make washed out colors look original
and bright again. You can also lighten up the image and include some details. Be careful as the surrounding areas of black can affect the histogram. The Clone Tool will handle tear damage and spots. You'll find nice tools in PhotoDeluxe, PhotoImpact, Paint Shop Pro or Photoshop.

http://www.scantips.com/restore.html

A computer, a scanner and reliable graphics software is everything you need to preserve your old photos. Clean the photos and the scanner before proceeding. Then select the type of scan (color or black and white). The images should be stored at a minimum of 300dpi if you want to store them on CDs or DVDs and you want to enhance them too. The photo should be placed face down on the glass. Crop the preview to include just the
image if the scanner doesn't automatically do that. Don't correct while scanning. See whether you have enough free memory and adjust the scan resolution, then allow a few minutes for the scan.

http://genealogy.about.com/cs/digitalphoto/a/digital_photos.htm

Old photos can be digitized and restored with tools such as the histogram for restoring contrast and the Clone Tool that can fix damages. After you scan it, you can use Black & White Points. Most of the times it's easier to repair stains in color mode. You could also lighten up the image and include some details. Be careful as the surrounding areas of black can affect the histogram. Just clip the tail of pixels off and experiment with contrast to make washed out colors look original and vivid again. The Clone Tool can handle tear damage and spots. You'll find useful tools in Paint Shop Pro, PhotoImpact, PhotoDeluxe or Photoshop.

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http://www.scantips.com/restore.html