The George Eastman House website has recently put online 31
images of Mark Twain from their collection.  Some appear to
be previously unpublished.  The URLs for the photos (which
can be viewed in larger sizes as well as "thumbnails") are:

http://www.geh.org/ar/twain/twain_sum00001.html

and

http://www.geh.org/ar/twain/twain_sum00002.html

Barb