It seems like the homescreen notification doesn't disappear, even after you delete the message. So if you wanted to do this for real, you'd have to use body paint or make your nipples transparent in such a way that your exposure can't be seen in the thumbnail itself.
I haven't ever used anything like this, so I was researching it while I was drawing this image. There might be a few inconsistensies in the way the image appears to the other person, and other things like that.
What I'm worried about is whether or not the thumbnail will show up on the homescreen notification even after the message has been deleted if the person who receives the message changes their notification settings to include the thumbnail on their homescreen afterwards. (If this is the case, then these girls lost as soon as they sent the selfie, lol)
If someone knows of a tool that is more suitable for these kinds of games, please let me know.