Hey Greg!
I'm sorry that I didn't see it was you posting the question initially. All great questions and I'm looking forward to seeing the others respond. I would definitely keep the images and find ways to incorporate the older or obsolete images into new content on the website. If people are linking to them, they find them valuable.
Another option is to 301 redirect the image URL to the page and place the image on that page. You would then get the equity from the image link to the page.
I hope that helps!