All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
First of all, we praise Allaah for guiding your friend to Islam and we ask Him to make him steadfast on this religion.
As regards him hanging a picture of his wife in his office, this is not permissible for two reasons:
1) It is forbidden to take pictures and hang them; there are Prophetic narrations which prohibit this. Please refer to Fataawa 84583 and 82040.
2) Hanging the picture of the wife is evidence that the husband is not jealous about his honour and dignity. The Prophet said: "There are three kinds of people who will not enter
Since this man is a new Muslim, it might be that he does not know the religious ruling. So you should advise him with wisdom and in soft words and clarify to him that this matter is forbidden in Islam as it advocates the protection of one's dignity and honour, lowering the gaze and avoiding anything that could lead to fornication or adultery. You should also advise him to call his wife and family to Islam. He should do his utmost in this regard as he might save them from Hellfire.
Allaah Knows best.