While you don't need to follow MLA or APA or any other citation format to credit images or other media on a website you still need to credit the original source material regardless of what permission was given to reuse it or how much it was modified from the original.
Creative Commons states:
A good rule of thumb is to use the acronym TASL, which stands for Title, Author, Source, License.
Depending on where you find your images, the creators may want you to include other information. For example the Library of Congress asks that you include the name of the collection within the Library of Congress the image belongs to (e.g. Wright Brothers collection).
See the links below for more information on best practices for crediting sources along with examples for various license types and media.
The Univac image is from the Library of Congress.
The Library of Congress tell me how they would like their images to be credited:
4. How should I credit the Library as the source of the images I’m using?
When material form the Library’s collections is reproduced in a publication or website or otherwise distributed, the Library requests the courtesy of a credit line.
Ideally, the credit will include
I created the following credit (which includes more information than they require):
[One man looks on as another man prepares Univac computer to predict a winning horse]. World Telegram & Sun photo by Herman Hiller, 1959. Library of Congress Prints and Photographs Division. New York World-Telegram and the Sun Newspaper Photograph Collection. LC-USZ62-118471.
