This came up in my RSS feeds today:
NY Public Library releases 180,000 free public domain pictures
Apparently, the images are all out of copyright, so you don't need to ask permission to use them. And with a collection that large, I suspect that there are going to be at least some which would prove useful to Wikitreers.
Unfortunately, we can't use photos from web sites in the SAT.
Alas, no. The participation rules for the Scan-A-Thon say that you can only count images that you have in your possession and scan yourself. I was all disappointed to hear that, because I thought the SAT would be a good chance to add images to a bunch of profiles of notables.