Use "include page" to include image for CustomField?

Is it possible to make “include page” on a CustomField able to display an image?

Currently if I specify a URL that’ll fetch an image it’ll just spit out the contents of the file and not treat it as an image. If I specify a URL that’ll fetch an HTML file that uses “img” to load the image then it is displayed. I’d rather not have to create dummy HTML files for each image…

Cheers,
Andrew