No way to attach image to related content item

I just noticed there's nowhere to add an image(s) to a related content item(like in a "More information" or "If you go" box). There are many instances when our break-out boxes have images. I may be missing something, and if so, please tell me what I'm doing wrong.

I tried adding an <img> tag with the image but BLOX seemed to have stripped that out.