Sending sexy pics in jail🐱👮🏽

So my boyfriends locked up and when I write him letters he likes me to send him pictures, some normal selfies and some risqué ones. I thought they were sexy but he wants sexier, I don't really know how to do that when I'm not allowed to show nipples or 🐱 in the pic. He said I could use emojis to cover them but I just don't know how exposed he wants the pics, he said he wants to be able to jerk off to them. I just feel like I'm so bad at being sexy. What do you think guys really want to see in a sexy pic?