The NYPL Gallery includes images and maps from the Russian empire between 1730 and 1935. See especially:
The Hoover Political Poster Database can be searched by country, artist, year or decade of creation, and subject (use Library of Congress Subject Headings, not keywords).
The Semyon Fridlyand Collection has digitized over 10,000 photos of life in the Soviet Union (1940s-1980s). Images browseable by title or date.
The International Institute of Social History has visual collections that you can search by country, theme, or keyword.
Below, you can also search Colby's subscription to ArtSTOR: