Billboard Ad Database

The Outdoor Advertising Association of America (OAAA) has compiled a database of billboard and other outdoor advertising images, like this one for the Wisconsin State Fair.

Alpha browse by topic or company name or search by keyword, year, agency, advertiser and/or product category.
For a little advertising history, try Duke University’s Emergence of Advertising in America: 1850-1920 database of historical images.
Source: ResourceShelf