First off, the obvious bit, which you've already hinted at: if the OP didn't like your edit, and his post wasn't breaking andany SE rules, then he's within his rights to reject your edit for whatever reason he wanted. (While legally, the posts are CC-licensed and editing it explicitly permitted, SE has a very long tradition of deferring to the OP's intent whenever possible.)
Secondly, while I'm not sure why you thought removing images from a post where they were relevant made a "good edit". The OP added those images for a reason, and the general opinion (based on voting patterns) is that images improve answers, not detract from them.
SE's software allows users to make edits to other users' posts to make it easier for us to improve them. We can fix grammatical/spelling errors, improve markup, insert references, etc. without needing to wait for the OP to come back. oweverHowever, what we shouldn't ever do is change the basic meaning/content of someone else's post without good reason.
The OP wrote their answer based off of specific information, and felt that including actual images of the script improved their answer. There's any number of reasons they might believe that, anywhere from authenticity to simply being cool. Editing their answer to remove such images does border on a "too substantive" change, and I would likely have rejected that kind of edit myself if I had access to the review tools.