No list of image collections can hope to be comprehensive. Below are some big collections we think you'll find especially useful, but consider trying some of the important catalogs to digital resources on the Web:
The Library has produced several collections of digital images--these collections include historical maps, German emblem books, French World War I posters, and Irish cartoons. These collections are available at http://images.library.uiuc.edu/projects/
The Library also has some unpublished primary source material (archives and manuscripts), but this is a relatively small body of material compared to the abundance of published primary sources held by the Library. Most of the unpublished primary source material will be found in the University Archives, located in the basementof the Main Library, or the Student Life and Culture Archive, located east of the President's house on Flordia Ave. in Urbana (1707 S. Orchard St.). More information is avialble about the holdings of the University Archives and the Student Life and Culture Archive at their website: http://www.library.uiuc.edu/archives/ , and the archisists can help you identify material on your topic.
There is another type of archival material in the Library that you might want to explore: if you are interested in advertising images, the Library holds 3 major collections of print advertising. The Communications Library curates the D'Arcy and Woodward Collections. The D'Arcy Collection contains 2 million ads published between 1890 and 1970, and the Woodward Collection contains 4 million ads from the late 19th century through the 1980s. In addition, the University Archives houses the Advertising Council Archives. The Advertising Council was established in 1942 to support the war effort through public service advertising and continues to operate today.