create alias extraction -> extraction_(image)
The term "extraction" by itself probably doesn't immediately bring to mind the idea of an extracted image for most people. I know that when I saw it on the tag list of the main post page, I first assumed it was for pictures of someone pulling teeth, or evacuating an agent, or carefully fishing something out of a hole, or something like that.
I was initially going to suggest "extracted_image" as the alias, but in case I'm completely wrong, and "extraction" really is the common term for the practice, I didn't think it would be right for me to demand that everyone else had to use something wildly different just because I thought their term wasn't clear enough.