4Walled.org uses a bot to search for backgrounds & posts them in a database
About 4Walled.org
Using the idea behind 4scrape, 4walled uses a PHP script to parse and download all the images posted on the boards. It checks if that image is already in the database, and then if it isn't it inserts them into the database with all the information it could get from the board. If the information is limited then the image gets marked as needing tags, which is when it appears on the help site. You won’t find those particular images by searching the database.
