Find images no in use

Site URL: https://www.seasonstoo.com

Hello,

early on we uploaded a lot of images into a gallery, which powers others pages via tags and categories. A year later, I would like to scrub the gallery for any images not in use and delete to free up space for new product.

Is there a way to find a list of images not in use on the site (i.e. no other page uses that ID)? Ideally, I would also like to delete in bulk, but at least finding the set would be a good start.

Thanks!