Is it permissible to photograph a segregated wedding party, and to photograph the wife while fearing her exposure to foreign men? And is the wife sinful if pictures are taken of her surreptitiously? And should she wear the niqab on her wedding night?

It is not permissible to photograph women if the pictures are likely to be seen by non-mahram men. Therefore, it is not permissible for you to allow anyone to photograph your wife if you know that the picture is likely to be seen by non-mahram men. If you and your wife take all possible precautions, and then a woman photographs your wife without her knowledge, there is no sin upon you or upon your wife.