Block unwanted sites from your Google, DuckDuckGo, Startpage.com, Bing and Yahoo search results. v2.2.8 2023-07-19
< Feedback on Google Hit Hider by Domain (Search Filter / Block Sites)
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.
DuckDuckGo images search
please add a button to block sites when searching images in DuckDuckGo