In Islam if a man watches a lady's picture and masturbates himself then who will be the sinner the man or the lady?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Masturbation is forbidden and if a man deliberately masturbates, then he is sinful regardless of the issue of the woman in the picture because of whom he masturbated.

It is foolish and nonsense to think that the person who deliberately ejaculates in a forbidden manner is not sinful and that the sin is on the woman who is in the picture; or that she shares the sin with him. We do not think that any sound-minded person would say such a thing.

With regard to the ruling on taking a picture of a woman and the extent of her sin in using her picture in what is forbidden, then this is a broad issue, and it is not useful for the person who committed what is forbidden because of the picture to know such a ruling. No matter what the ruling is regarding her, this does not rid the person from sin.

Allah knows best.