If you look at the url of one of your posts here you can see it ends with a number about this long: 38760522 (<— Example from one of my own uploads)

If you post that number in the ‘ID’ section of a comm listing it will use that image. If the artwork is NSFW then depending on the settings of a certain user they might not see the image, so I recommend using SFW art for these.

Hope this helps!

tysm! ^v^