In certain cases, you may run the Find Duplicates command and see some duplicate groups where the photos don’t look the same. There can be a few different ways this can happen.
Original vs. edited
Whenever you edit a photo in Photos, it keeps a copy of the unedited original behind the scenes, and creates a separate copy of the photo with your edits, which is the one that’s displayed. If you have two copies of the same photo in the library, and one has been edited and the other has not, then you can end up with two photos that look different side by side but have been matched as duplicates because they’re based on the same original photo.
If you don’t want such matches to appear, make sure to select the “Compare current photo” option under “Exact match”, and disable the “Match on filename + date” option. That will make sure that PowerPhotos only matches photos that are 100% identical, including edits
Filename + date ambiguity
In many cases, you may have two copies of a photo in the library that look the same, but are just a little different, and thus don’t qualify as an exact match. This is what PowerPhotos provides the “Match on filename + date” option for, which looks at those two pieces of metadata on each photo rather than comparing the actual photo data.
The date is included because it’s very common for two completely unrelated photos to have the same filename (e.g. “IMG_1234.JPG”), but such pairs of photos will almost always have different dates. There are also times when the filename has been slightly altered (e.g. “IMG_1234_2.JPG”), which PowerPhotos provides the “Allow filename variations” option for.
However, in certain cases, there can be photos that have similar filenames and identical dates that end up being matched as duplicates. The most common scenario is a series of scanned photos that don’t have any embedded date from a digital camera, and have all been assigned identical timestamps. If the photos also have very similar filenames (e.g. “scan_20210330_1.JPG”, then they may end up getting matched as duplicates. This can also happen with certain photo editing software that goes awry and assigns identical timestamps to a whole batch of photos.
If you see this type of thing happening, first try disabling the “Allow filename variations” option, so that PowerPhotos will only match photos whose filename are completely the same. If you still see dissimilar photos being matched, then try disabling the “Match on filename + date” option altogether.