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Are those domains in the Google index?

Have you tried "site:example.com" for the sites you're mentioning?

I haven't had to do this myself but I've heard that that's what you try.

If those sites aren't indexed then they probably are no good.

In the Yoast SEO Plugin there is a setting under Permalinks, that says this.

Redirect attachment URL's to parent post URL?

"Attachments to posts are stored in the database as posts, this means they're accessible under their own URL's if you do not redirect them, enabling this will redirect them to the post they were attached to."

So it whether you're using images in WP as normal attachments or in a lightbox, I would still check this box and have them redirected. I don't know all the details around this but this is what I do.

Tried to attach an image to show you, but not sure if it worked.

seo-wp-images.png