Who is this?

Today we have a true mystery at the Latah County Historical Society.  I was recently gone for a week and this picture arrived as a donation while I was gone.  I am hoping to solicit help from anybody who might be able to identify the person in the picture or any information about it.  We know that it was purchased at a barn sale about 25 years ago and on the back of the portrait is the word Clarke written in pencil and cursive script.  I am considering this item for accession, however I know nothing about it.  If you have any information please contact:

Zach Wnek
 Museum Curator
 Latah County Historical Society
 208-882-1004
 zwnek(at)latah.id.us