The color photograph I mentioned earlier is the first photo and the
first photo of Twain in a long (37 pages) article entitled "Mark
Twain: Mirror of America" by Noel Grove, appearing in the
September, 1975, issue of -National Geographic Magazine- (Vol.
148, No. 3).  The caption reads in part: "Doctor of letters, student
of the world: Wearing the robe in which he received an honorary
degree from Oxford University in 1907, Mark Twain poses for a rare
color photograph, published here for the first time."  The picture is
credited to "Alvin Langdon Coburn, courtesy Mark Twain Memorial,
Hartford, Connecticut."  Perhaps, one can gain permission from the
MTM for its use on book covers.

In the photo, Mark Twain stands in profile looking out a window, a
cigar in his right hand, his left in his pocket, pulling back the robe
to expose his white suit beneath the gray and red Oxford gown.
His head, wearing a black mortarboard, looks very much like the
one Bill Watterson drew for the -Mark Twain Journal- that appears
on its stationery and T-shirts, though Twain looks more
contemplative in this portrait.

I hope that you find this information helpful.

John H. Davis, Ph.D.
Chowan College
Murfreesboro, NC