I recently did some searching on E-Yearbook.com. For a fee, you can search this database and access many old high school and college yearbooks. Be prepared, though--the list of American institutions represented is not a complete one. You may not find a digital copy of the Podunk College yearbook for your great uncle's graduation class. Still, there are many treasures to be found, and if nothing else, the database contains a good slice of social history research for those interested in campus life throughout the decades.
E-Yearbook.com does a lock-down job of protecting copyright interests by ensuring that images cannot be copied or altered. I wish the database were set up to be a bit more share-friendly, but it is a useful research tool, just the same. For example, their digitized collection for Blue and Gold, the yearbook for the University of California at Berkeley (CAL) goes back to 1875!
I was searching for images of members of my father's family (Wheeler and Thaxter surnames), and came up with a few gems. The indexing of E-Yearbook.com is not perfect, and I sometimes found that an image resulting from my search was not the image of the person I was looking for, due to an incorrect link. But, with a little sleuthing around, you can still find what you are looking for, particularly if you have an idea when a person graduated. Be aware that the image numbers do not correspond to page numbers in the actual yearbook.
I'll give an example of a typical search challenge. I found evidence that my father's uncle, McKinley Wheeler, was a graduate of UC Berkeley's class of 1920. Doing a search on his name in E-Yearbook.com brought up nothing initially. But, while scrolling through the pages of student photographs, I found him identified as "McK Wheeler" in the yearbook because of lack of print space. To make things worse, the text added by an indexer at the bottom of the image contained a mistype of his name as "Me K Wheeler." The moral is: use your imagination when searching old documents, and try as many crazy spelling combinations and/or abbreviations as you can think of.
While searching, I found wonderful caricatures of some students and faculty (pages 50-53 of UC Berkeley's class of 1929 "Blue and Gold" yearbook: indexed as images 62-65). I wish I could share them, but you'll have to take a peek for yourself!