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please add a button to block sites when searching images in DuckDuckGo
The image results on DDG do not have the site URL encoded with the thumbnail. Instead, the URL is part of a data structure DDG retrieves in the background when you load the page, and consults when you click the thumbnail. I can't figure out how to access that data.
That sounds like something AdBlockPlus or Disconnect could do rather easily. Assuming that the images are all actually coming from the same domain.