A search of the Corbis site finds that the company claims copyright to the image (IH081187|Rights Managed|Image:© CORBIS). (The price charged depends on usage: full page inside an academic journal with 10000 circulation in Australia costs around 280AUD, web use for a year plus archiving is 220AUD.)
But the Library of congress site tells another story.
"There are no known restrictions on the use of Lange's "Migrant Mother" images. A rights statement for the Farm Security Administration/Office of War Information black-and-white negatives is available online at: http://www.loc.gov/rr/print/res/071_fsab.html."
The image that is digitally reproduced above is from a film copy negative (LC-USZ62-95653)--it is not retouched and "This version of the image shows a thumb in the immediate foreground on the right side." The retouched version is also available for download. It's Library of Congress copy looks like this:
What is Corbis claiming a copyright on? Are they claiming a copyright on the specific copy (print) that they own? If so, does their claim effect other copies?
Or, is Corbis charging for the service of clearing the rights which as the LofC warns elsewhere
" researchers should be advised that determining the copyright status of photographs can be problematic because of the lack of pertinent information, and researchers often have to make calculated risk decisions concerning the appropriate use of an image when its copyright status is unknown or ambiguous. Privacy and publicity rights may also apply."
(I've been thinking a lot about photography recently, having picked up my copy of Looking At Photographs: 100 Pictures from the collection of the Museum of Modern Art by John Szarkowski (MOMA, 1973, 1999))