didnt get here in time but I've played with a few free php based ready made image galleries that take all the hassle out of building one from scratch - especially if a) you dont have time to code a full featured system or b) you dont know much about it all.
https://gallery.menalto.com/
https://coppermine-gallery.net/

both are web-based and do what you expect - web-based interface for creating and editing galleries and uploading content. They also auto-generate thumbnails and you can tag content and export it out etc.
Anyways, more for reference now

Si