Yes, Getty Images should be sued in this case. The images were donated so that everyone can access them for free. That's how it works. When Getty Images takes something it acquired for free and then tries to sell it to make a buck, it's being greedy, and a lawsuit is justified.
Whether the images are donated or not, they are the intellectual property of the photographer unless he's specifically assigned those rights to Getty Images. Also, it's unclear what the terms of the donation are. For instance, a photographer may donate images to with the understanding they're free to use so long as they're published with an attribution that credits the photographer and Getty.
Photographer Carol Highsmith has every right to sue Getty Images for the illegal selling of more than 18,000 photos that she had donated to the public for free through the Library of Congress. Highsmith owned the rights to the photos and chose to pass those rights to the public. Getty Images and other companies misappropriated her work and began illegally charging for them.
No, the photographer is not justified in suing Getty Images. It is my belief that, regardless of whether the images were donated or sold to the company, they are now the property of the company. If the photographer desired that the donated images were not sold, that should have been specified in a contract of some sort when the images were initially donated to the company.