You could make a vine of you deleting it against his wishes and keep that even after fighting and (hopefully?) resolving any hard feelings he has about it. Juuust kidding.
Are you worried that if he can look on it fondly while you only see a memento of when he hurt you, that he can't be trusted to not do it again? Because if that is how you feel then the picture doesn't matter - you just don't trust him and you can't heal under that condition. The picture being gone won't make that moment in time go away. Him keeping it implies something threatening to you. Get rid of him or decide he is worth the risk. The picture isn't the real problem.