How does Instagram load their images?

I had an interesting thought about image privacy. Say you make your S3 bucket public while creating a social media platform so people can see images. If you have some sort of "private account" feature, how do you make sure people not following can't directly view the images associated with the private account?

X/Twitter does not care. I have this image posted on my private account and can view it in incognito no problem [https://pbs.twimg.com/media/GrhpPLoXkAA4ZuP?format=jpg&name=4096x4096](https://pbs.twimg.com/media/GrhpPLoXkAA4ZuP?format=jpg&name=4096x4096)

Instagram however, does not have this "copy image address" on their images (on the web version btw). How are they getting around including an <img> tag in their frontend? Also, if you were able to access the image, is there a way to programmatically accept/deny access based on if they're following or not?