If they're *only* in iCloud then you'd be better of logging in to the iCloud.com web portal on a computer and doing it there. You can Ctrl+Click to select more than one at a time and you have a much bigger view.
I would personally do it on my Mac over my iPhone, but I have used Slidebox a few times. It keeps track of what folders and photos you've already managed and is a lot quicker than the photos app.
Organize your photos with quick & simple gestures! - Delete: Trash unwanted photos with a swipe of a finger - Organize: Sort photos into albums with a single tap - Compare: Swipe similar photos back and forth to compare - Favorite: Mark special photos as your favorites Slidebox interacts...
Download Remo Duplicate Photos Remover by Remo Software on the App Store. See screenshots, ratings and reviews, user tips, and more games like Remo Duplicate…
Download Remo Duplicate Photos Remover by Remo Software on the App Store. See screenshots, ratings and reviews, user tips, and more games like Remo Duplicate…