Comment 3 for bug 1752448

Feel free to word the new message in whatever way you feel is more correct. The current message is definitely incorrect.

Your suggestion is fine with me:
libcupsimage2 : Depends: libcups2 (= 1.7.2-0ubuntu1.8) but 1.7.2-0ubuntu1.9 will remain installed.

Whether it is installed or not matters a lot to someone trying to understand why they are getting an error message. As a package management utility I'm sure apt should be able to detect what is installed and give an appropriate message for either case.

If you think adding additional detection would overcomplicate the code then a more inclusive message could work too but is a little harder to read:
libcupsimage2 : Depends: libcups2 (= 1.7.2-0ubuntu1.8) but 1.7.2-0ubuntu1.9 is to be or will remain installed.