If you believe that your frame is showing photos that you had never added via the Aura app, this can be due to the following:
1) Somebody who is also invited to the frame added the photo
Anybody that you have invited to your frame can upload new photos to your frame via their Aura app. If you own an Aura model that comes with a Touch Bar (Mason, Sawyer, Caver, Smith) you can tap on the top of the frame to display additional photo information, including who had submitted that photo to your frame.
2) The photo was part of an album that you synced with your app
If you upload an entire Album or Smart Album via the "Add All" function, Aura will not only select all the photos in that album to display on your frame, it will also automatically select any new photos that are added to the album. For regular Albums, this just means any photos you add to the album on your phone. Smart Albums, however, are collections of photos that Aura has curated for you. If you select "Add All" for a Smart Album, anytime you take photos of that person it will also get added to your frame.
You can view all of your selected Albums and Smart Albums by tapping into the "Frames" section in the Aura App. Next, tap on your frame name to view albums at the top and individually selected photos below.
You can remove an entire album by tapping where it says "Edit" and deselecting the frame to which it's been added.
There is also an option to "block" the album entirely or "hide" individual photos from the album. To do this, tap the icon on the top right (three small dots) where you will see the option to "Hide Photos" or "Block Album." Selecting to "Hide Photos" will allow you to check and remove individual photos from an album however "Block Album" will remove the album entirely.
To remove individually added photos from your frame, tap into the frame and click the Edit button. Then select the photos you'd like to remove before tapping "Hide Photos."