I have Google Photos app on my phone set up so that every picture I take with my phone ends up also on Google Photos online. Sometimes, however, it asks me if I want to free up space on my phone by deleting them from my phone and they will still be in Google Photos online. My question is this: When viewing my Google Photos online from a web browser, or from the Google Photos app, is there a way that I can easily tell which of the photos I am seeing are actually only in Google Photos online, versus which ones are also stored on my phone?
Unfortunately, the answer is no. In order sync to work, Google Photos has access to your gallery and camera on your device, and your device has granted access for uploading to Google Photos. And here it ends. Your device has no means to backcheck against the online gallery and let you know which ones are there and which aren't. Also the same applies to Google Photos - it doesn't backcheck against your device gallery and send you a notification flag of the status nor it keeps/creates logs by spying on your device's gallery.