You are just not sure if they are really duplicates
It comes up with groups of thumbnails which I suppose are duplicates but they do not show as duplicates just a single image. You mark them for deletion then review them. What exactly are you supposed to review as there is no comparison to the one it decides to leave. I would prefer to see the duplicates side by side then mark them for deletion. I would have expected it to take an hour or so to check 11,000 images but it took no time at all just instantly appeared on the screen. I have given it 3 stars for ease of use but dare not mark any and delete them.