Google Photos is by far the best tool to save all of your pictures to; I even moved my Flickr library to Google Photos recently and I couldn’t be happier. The great feature of Google Photos, next to its easy to use interface, is the unlimited number of photos you can store. Since it’s unlimited, I often find myself dropping whole folders onto Google Photos using the web interface at photos.google.com.
However, I recently found out that I also have lots of duplicate images on the service. Since the storage is unlimited, it happens I upload the same pictures two times. To keep a clean pictures library, I was looking for a way to efficiently remove duplicates without manual work involved.
First of all, Google Photos will automatically recognise if the exact same image already exists in your library when you have enabled automatic upload. What this means is that if you have automatic upload enabled on the desktop or on a mobile device, the service will not upload any pictures nor videos that already exist.
However, when you manually upload pictures, you can upload one or more videos or photos that you already upload before – be it either via the automatic upload feature or also manually. The first solution would be to keep an eye out yourself and see if you already uploaded a set of pictures or movies.
The second option is to use the Picasa client. Get it at https://picasa.google.com/ and install it. Then, login into your Google account. You will now see that all of your Google Photos files will show up in the client. Enable syncing and then go to Tools, choose Experimental and click on Show Duplicate Files. Delete the duplicate files and sync your library again. Now any duplicate pictures will be removed from your library.
In the future, Google may introduce a build-in feature into their mobile and desktop tools that allow to remove identical photos and videos.