I never thought I'd say this, but I think Pretty just made the most intelligent post of the day.

There are lots of places to get mugshots:

http://www.ancestorhunt.com/prison_search.htm is a good start. Not all states offer mugshots, though.

http://www.ancestorhunt.com/county-jail-inmates-search.htm gets you to county jail sites.

Then there's the old reliable www.mugshots.com

K1ng gets most of his from Idaho, I believe, but I don't know the site.