Is there a way to add tags or keywords to a photo on iOS 11?
Ios11 does a pretty good job on search, but isn't perfect. I'd like to add tags to certain photos.
It used to be possible in iPhoto on iOS devices, but iPhoto is no longer compatible since iOS 8. And Photos can search for keywords that you add in Photos on a mac and sync with iCloud Photo Library, but it does not support to add keywords. You could try to annotate your photos with third-party apps, perhaps Meta Gear will do what you want:
MetaGear - metadata editor on the App Store
Photos will not show you the metadata you add, but you should be able to search for them.