If you often take thousands of pictures and then copy them to computer or to third party cloud storage, after all you need to clear your iPhones (or iPads) media gallery.
Using Photo Deleter app you dont need to select thousands of photos manually.
If you have already copied all media to your computer Photo Deleter can help you to move ALL photos & videos from your Photos app to the Recently Deleted folder. It will be empty in 30 days automatically, or you can clear it by yourself.
If you use iCloud and backup photos and videos there, in some cases your media content can be restored automatically back again.