This digital collection was put together by Lincoln Cushing, author of several books collecting political posters from various movements and regions. It has scans of all known OSPAAAL posters through 1995. OSPAAAL is the Organization in Solidarity with the People of Africa, Asia, and Latin America. The collection's intended audience seems to be revolutionary-types, scholars and history buffs who are interested in political struggle, but this collection would also be a great resource for graphic designers (with this caveat).
The site is organized simply, with thumbnails of the posters, and links at the top to skip through the collection by various countries, or "Che" and "Generic". There are 342 images in total. Most scans are 72ppi, though I found a few that were 100ppi. The lack of print-quality resolution fits into Cushing's approach of "digitization for access, not for preservation",which espouses "creating simple reference shots upon collection intake", with the idea of taking better scans at a later time, as needed/called for. Reinforcing this, Cushing refers to the collection as a catalog (though it's listed as an archive on the site).
Clicking on a thumbnail takes you to a scan's record, with a larger version of the scan, metadata, and a pop-up announcement stating, "Images on this site are copyrighted. All rights reserved. Use forbidden without prior permission being granted." This pop-up appears every time you click on a thumbnail. In the same vein, a blank .gif layer is put over all the scans (similar to the spaceball.gif on Flickr) to discourage users from right-clicking and saving them. None of this is out of line with Cushing's focus and protection of the artists, but there may be less obtrusive ways to accomplish the same goal.
In each record, there's a catalog number listed, named according to the geographic region of the poster. There's also the name of a .jpg listed at the top of each record that I hypothesize would go with the digital master file. There are additional fields for geographic region, country, year, artist, medium, size, and additional notes. It's a testament to Cushing's research that there are so few blank spaces for artists' names, and as a printer, it's really useful to know the print medium. There are some flaws in the collection, especially the clunky attempts at copy protection, but the objects are quite impressive.