Deep re-check
A second, closer look that drops the sets which only looked alike.
A RAW file and its JPEG are the same photo, but they are not interchangeable — the RAW holds far more information. Deduplo shows them together so you can decide, and never marks either side for you.
After a scan, Deduplo can take a second, much closer look at the sets it found and drop the ones that only looked alike. Sets it rejects move to the Ruled out view, where you can see exactly what it threw out.
This runs on its own after a scan. You can start it again from Toolbox ▸ Look again, harder.
Find copies of one photo
Toolbox ▸ Look again, harder answers a narrower question: do I have this particular photo anywhere? Point it at a file and it searches your scanned library for that one image.
Photos inside ZIP, TAR and 7z files
Tick Inside ZIP / TAR / 7z in the Scan setup window's Files pane and Deduplo looks inside zip, tar and 7z archives too. A photo already stored in one then appears in the set beside your loose copies — so you can see a copy is safely kept before removing the one on your drive.
An archive can also be scanned on its own, without the folder around it: press Add archive files… in the Scan setup window's Folders pane, or drop the file onto Deduplo. It is read as if it were a folder, whether or not the tick above is on.
A photo inside an archive can never be deleted, and its tick box is disabled. Taking something out of a zip would mean rewriting the whole archive, which Deduplo does not do — it only ever reads them. If a set contains nothing but archived copies, nothing in it is offered for removal.