Damn you, Firefox! I had just about completed this reply when Foxfire crashed and I had to begin again from the beginning.
The woman in that photo is Nan Wood Graham, sister of the artist, Grant Wood (1891-1942), who painted American Gothic. She died in 1990 at the ripe old age of 91. The man is Wood's dentist, Dr. Byron H. McKeeby, who died in 1950.
According to Wikipedia, the painting depicts a man and his spinster daughter, rather than a husband and wife as commonly assumed, but there seems to be some controversy about that. According to
this write-up on Flicker, Nan W. Graham grew embarrassed at being depicted as the wife of a man so much older, and so began claiming that the painting actually depicted a father and daughter rather than a husband and wife, while her brother remained silent on the issue.
Great find, patilsaurabhr!