Google Photographs does not have an automatic mechanism of detecting duplicate photos, but its search feature makes it a little simpler to find them. Google Photos examines all of your photos and assigns labels based on what they contain. As a result, you may search for keywords like "sunset" or "Napa Valley" without having to manually add tags. In principle, you could detect if you had any duplicates just by reading through your search results. On your iPhone, go to the Google Photos app. At the bottom, click Search. Type in a phrase like "beach" in the search bar. Hold down the mouse button over the image(s) you want to remove.