Occasionally I wind up with large numbers of duplicate images due to importing something multiple times over a period of months or years. Literally, importing the exact same images, but for whatever reason, import doesn't notice that they're duplicates. File name changed, date changed, I don't know. When I wind up with "-4" filenames for 5 copies of the same image, I feel like something isn't working right.
I really want to be able to find images that are certainly duplicates and that are almost certainly duplicates, and do something with them.
Certainly duplicates means the same bits in the image. Lightroom does not work this way however. I'm not sure exactly what way it works.
Almost certainly duplicates or just "very similar" means:
Very strong likelihood JPEG/raw match (e.g. if same filename and feature-similar image, some metadata matches, etc etc)
Same for TIF/PSD/JPEG/raw etc etc
Same photo resized, reoriented
Same photo cropped a little
Same photo with watermark/steganography
Same photo with border
I could see how "smart collection" could be a good way to integrate this into the application. Make a collection of photos with X attributes and filter out the ones that aren't duplicate or similar.