Informit.com has a detailed about repairing damaged photographs in Photoshop. It provides some very useful tips. It is divided into the following sections:

  1. 1. Starting Out Right
  2. 2. Working Smarter
  3. 3. Photoshop Tools
  4. 4. Creating Reversible Fixes
  5. 5. Performing Major Surgery Step-By-Step
  6. 6. Fixing a Damaged Print
  7. 7. Solving the Case of the Missing Data
  8. 8. Summary

The article link is: http://www.informit.com/articles/article.asp?p=418667&rl=1