I'm thinking of image_response as meaning exactly what it means on pixiv: an image created as a "response" to a prior image, one of the most notable examples being where someone draws an uncolored version of an image and various artists do their own rendition of it. It's also a familiar wording because even YouTube, I believe, has "video responses". That's what they're called, right?
Came across it most recently with post #509670. Couldn't figure out why it had two artist tags, and then realized why. Here's the original and three responses - link
Maybe it could also be used for pixiv projects like "expressions" and "hairstyles of my wife" and "let's make touhou kids", etc. I've only really thought it through in terms of the type of example I linked, though. So there could be downsides to other usages, and we might want to restrict it more, etc etc.
I'm not sure yet so that's why I'm asking. Thoughts?
Updated by Hillside Moose