Custom thumbnails for art have been broken for ages, at least ten years.

So how am I supposed to warn people that an art submission might be outside my usual fare, like something gory? Because right now with it being broken, the full image will show up in their inbox as a thumbnail.

About the only way I've seen is posting a cropped image, and a link to the full version on another side, but that doesn't really work if people don't have an account on that site. The truth is, I'm not sure there is a proper way to do that here.

For my kind of on the edge stuff, I will at least put a warning in the title, but that really doesn't stop it from showing up.