Hi swelljoe, sorry for the delay in responding.
Google image results have a Content Security Policy that blocks the script from being inserted by Violentmonkey in Firefox. It should work in Tampermonkey, Greasemonkey, or FireMonkey. I haven't had time to dig into how to modify the script to make it work in Violentmonkey.
For DuckDuckGo, I'll need to study the page layout to add support for image results.
On both Google Images and DuckDuckGo Images, results from blocked domains continue to show up. The
blockbutton also doesn't appear on Images pages.