Doco was a wonderful help (when it worked!) if one had multiple images open in separate tabs simultaneously.
It worked on a Mac up to Mojave but Catalina killed it; and I understand that it is now problematic in Windows as well.
Unfortunately its Developer seems to have lost interest in it because he has not updated it and doesn't respond to eMails either.
Until Doco gets updated, I can really not recommend it unless you intend to stay with an older OS.
Also, it does cost $10 with apparently no way of getting a refund if it doesn't run on your System.