Image URLs in feeds

I’ve been working on a JSON feed client and I am confused about the image URLs. If I view my feed using a web browser at micro.blog, then click on an image and select “Open image in new window”, the URL of the image looks like this:

https://micro.blog/photos/1000x/https://elegantnewt.blog/uploads/2021/bf9938c398.jpg

I’m also seeing the double-https URL for image tags when my test client downloads the feed.

Does anybody know why the feed is adding the “https://micro.blog/photos/1000x/” prefix to the image URL?

Thanks,
Carl

That’s using the Micro.blog api to set the photo width to 1000 px. The original is at https://elegantnewt.blog/uploads/2021/bf9938c398.jpg.