Your boyfriend might have felt repulsed by sending a half-naked picture of you to him. He should have told you about it instead of breaking up with you.
Send him a text or call him (if he'll pick up the call) and tell him you didn't know he was repelled to such kind of a photo. Apologize. If he doesn't respond or responds negatively, cease any contact with him for two weeks.
If he doesn't respond during no contact or you contact him after two weeks but doesn't respond or responds negatively; you'll have to give up the relationship. It will be time to move on because it might be there's a deeper reason he broke up with you and not necessarily because you sent him such a photo.