Linux

Hello! I have a bunch of photos all mixed together, and I'd like to sort them out in order to better find the ones I'm searching for without loosing half an hour. I was thinking of adding custom tags to each image (manually), like "my dog", "trip to Paris", "my friend X" etc. I'd like this tag system to be portable, filesystem-indipendent. What are my best bet?

On dolphin if I click on a file I can add a custom tag. Where is the tag stored? in the file or in some plasma configuration file, so that moving the file on my phone would loose the tags?

I searched the web but probably I don't really know how to call this, because all I found was a bunch of 11 years old threads or video tag editor (I need to do this with images)

thanks in advance!

EDIT: I have a HUGE amount of pictures to sort manually, so I'd need a GUI designed to be really quick. It probably does not exist, or if it does it won't satisfy me, so I'd probably write my own simple frontend for it, so the ideal would be a CLI tool or something QT-compatible