I've noticed that the Gallery Addon provides an 'attachment' page which I assume is for SEO purposes. I think it's part of the Spotlight lightbox maybe.
Without this, Google indexing wouldn't be very good, so it's great have this.
I've attached a screenshot of an example for reference.
The suggestion is to improve the page.
1. Insert the image caption/description as the page meta description, and also as text on the page itself.
2. Remove the username above the image.
3. Make the 'Previous Media" link go to the full image gallery, or provide a button leading to the gallery. When I click the link, is does nothing.
4. User a little bit larger image on the page, or maybe provide some options for the page in the plugin settings.