Is your husband making a big deal about the picture or are you just wanting him to delete it? If he is making comments about it then I would say you have a right to ask. If he isn't making a big deal about neither should you.
It depends: is it a jealousy thing? If so, the picture is only part of the problem. Is it for your friend's sake? Then by all means, have him delete it. Why is he keeping this picture anyway? If he's friends with your friend, let him keep it. If he finds her attractive and that's why he's keeping it, you have every reason to delete it yourself and kick him out of your life!
Yes, ask him. If you're a Christian you know women should be dressed modestly in public, and a sexy photo might lead to lust and other problems. I agree that "If he loves you, respects you and only wants you, deleting a photo online would not matter to him, ever."