
To begin finding duplicate photos in your Photos libraries, either click the magnifying glass button in the toolbar, or select “Find Duplicates” from the Library menu. This will present you with a view to set up your duplicate finding.
There are two areas you need to set up to begin your duplicate search
What to search The Find Duplicates command can search one or more Photos libraries at once, looking for duplicate photos. To search a library, drag it from the library list on the left into the area labelled “Choose Libraries to Search”. To remove a library, click the X next to its name.
You also have the option to exclude certain photos from being included in the search. Click the “Exclusions…” button, and you will be given the option to skip looking at photos that are either already in the “PowerPhotos keepers” or “PowerPhotos nonkeepers” albums (e.g. if you performed a previous duplicate search already), are marked as hidden, or already have the keyword named “duplicate” assigned to them in Photos. Note that because OS X does not allow PowerPhotos to access hidden photos from the system photo library, hidden photos will never be analyzed when searching the system photo library, regardless of the setting here.
How to compare photos PowerPhotos has two methods that you can use to compare photos to each other and determine whether they are duplicates
Note that there can be some cases where there are two photos that look the same visually to the human eye, but are not actually identical, e.g. if one copy is a scaled down version of the other. Since they are not 100% identical though, the “Exact match” option won’t identify them as duplicates. The filename + date search can help find these sometimes, but if either one of those pieces of information has also been changed, then there’s no easy way left for PowerPhotos to tell that the two photos “look” the same.
Once you’ve set up your search, click the blue “Find Duplicates” button in the upper right corner of the window, and PowerPhotos will begin analyzing your libraries for duplicate photos.