1. Don't send ANYTHING to someone else unless you are willing to see it online for everyone in the world to see. That's -- unfortunately -- the world we live in today. What is private between a woman and her partner becomes public property and sometimes even a post for ridicule or to embarrass the other when they break up. If you get the urge to send him a revealing picture, call him on the phone and ask him to come over for a look...
2. TALK to him plainly. Tell him (a) If you ever post a picture of me on your social media, please check with me first; if you respect me, you'll respect my wishes. (b) If you want me to continue to be your girlfriend, you'll pay attention to (a). (c) If in doubt, refer to (a) and (b).
3. If your boyfriend sloughs this off as "Aw, you're being too picky. There's nothing wrong with those pictures, and you shouldn't complain because it's not a big deal..." Then know this: Your boyfriend doesn't really care about you. All he cares about is himself: how YOU make him look good; how he can brag to his buddies by saying "look how hot my girlfriend is--I must be pretty sexy to get someone that hot" (which, of course, isn't about you but about how hot HE is). If he doesn't respect your wishes, he doesn't respect you--even if he truly believes it's no big deal... he'll take the pictures down and won't post more like them in the future. Why? Because he cares about you. If he WON'T, then he truly doesn't care about you.
BOTTOM LINE: You'll find out very quickly what your relationship REALLY is with your boyfriend.