Advice please ?

Different couples have different “rules” about that. For many, the rule is: “it’s ok to look but you can’t touch.” He may be feeling like his needs aren’t being met because you just had a baby (and so he’s masturbating to not bother you while you’re healing—that’s healthy and considerate IMO). I think the most important thing is to communicate with him about your feelings, and also know that your hormones are probably going to amplify those feelings.

I’ve had three babies. I know it is just short of being a year of feeling like your body and time are controlled by someone else. You eat different, you sleep different, and so on.
It is rough for the men too.
One minute he can look at you and see a beautiful woman who is going to bring his child into the world. A minute later he might see you as a gigantic pig, and wonder why he ever hooked up with you from the start.
Most men are confused about what is going on in your head and body, how they should behave around you.

If he is only looking, then let him have it. It can give him a sense of normalcy.
If he is doing more than window shopping, you should have a talk with him.

It isn’t “wrong” for you to be upset. Your question is like asking “is it wrong that I’m sleepy or hungry?” You ARE upset, and asking us to weigh in on the matter with scant knowledge of you, the boyfriend or the circumstances of the search or even your relationship. For example, is your boyfriend the baby’s dad? Have you talked with him about his “hobby”? In the end though, it probably doesn’t matter how much information you provide us. To my mind, if looking at pictures is the extent of his “transgressions”, you are probably fortunate. You must realize that there is no undertaking more difficult than the regulation of another’s fantasies. You know him best. Why not try pointing him toward things you believe might interest him more. For one thing, dealing with a newborn should keep you both so busy and sleep deprived that…you get the picture.