Definitely worth contacting support about, then....for emotional support, if nothing else! And unfortunately, removing a course card image from the Blueprint master won't work, either. (I just tried it....even after changing some text on the front page to help kickstart the sync command that something changed in the course.) One reason, I fear, is that settings are not "blueprintable" in that while you can push over the settings to the associated course, there is nothing to prevent an instructor from changing them on their own. One would think, however, that removing a setting would work in the sync, as well. No such luck.
I do think blueprint courses are a really cool feature in Canvas, but understanding all the idiosyncrasies are vital to a successful rollout, so it's good that you're trying out some things now! (Not that my words will help remove 23 course card images.)
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