I have tried creating a 404 image that is the image I want. I did this because I noticed if I upload an image to the site and then type out the name of the image I want on the URL path, it embeds properly. Creating this 404 page did nothing and the link still did not embed.
I have an image I have uploaded onto the site. When you post a link that goes directly to an image file on discord, it removes the link and instead just shows the image. an example would be if I posted a raw Imgur image link. If the image ID was valid and it led to a gif/jpeg/png, discord would just hide the link and show the image.