Once you've finished collecting and are back home and uploaded photos, you can see them in your gallery.
To do that, go to the Profile tab of the app. This will show your total litter count as well as a map of your impact.
In the bottom section of the profile screen, you will see the Gallery option to see each individual picture you've uploaded.
From there you can view your uploaded photos. There's a tab that will allow you to view your untagged items.