Although it's not mentioned in the question I assume it's not a photo of his wife alone. If it's a picture of his daughter with her mom or of them as a family.... he may mean what he says.
It doesn't sound like he hid the picture to begin with. So how did he become this woman's husband if it bothered her?
One should not wait until after someone becomes emotionally invovled let alone married to start complaining about something that was always out in the open. Marriage is about loving and accepting someone for who they are, quirks and all. The whole purpose of dating/courting is to find out if you can dea with each other's baggage. Unless the wife has reason to believe her husband is still "in love" with his ex then it's not anymore of an issue today than it was while she was dating him.