There are lots of places on the internet that have archives of old photos (I found the above picture of my Great great Grandpa on ancestry.com) Here are a few places to start:
1. www.familyoldphotos.com - On this site you can search their archive and link to other archives. They have civil war photos and much more.
2. www.ancestry.com (public member photos and scanned documents)
3. Cindy's list - follow link below and click on photo archives