No, unfortunately, this cannot be turned off, and nothing suggests that this is fixed in the release notes for Xcode 8.1 .
This should either be fixed, or you should be able to disable it. Functionality is very good when it is used only for its purpose, as I describe in this publication.
But the problem is that Xcode 8 inserts images embedded in the source when it cannot make any sense, as you mention. For example, if you have an iteration and enter for x in to start the loop, and you have any image in the project whose name matches "in" using this syntax.

Annoying problem, I hope Apple fixes it soon because the feature is good when it is used only for images.
Update :
Just confirmed that this is still a problem in the stable version of Xcode 8.1.
Update :
This functionality remains in Xcode version 9.0 beta 6 (9M214v) 
Rashwan L Oct 26 '16 at 10:58 2016-10-26 10:58
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