Is it permissible for a man to masturbate by looking at his wife's picture only, without using his hand? And is it permissible for a woman to do so, especially if one of them is absent from the other for a long period?

It is permissible for spouses to enjoy all parts of each other's bodies by any means, provided that it is not in the anus or during menstruation or during the state of ihram for Hajj or 'Umrah, and provided that there is no risk of others seeing them. One should not be excessive in this matter so that it does not lead to forbidden masturbation, especially for one who is away from his wife. He should occupy his time with beneficial things and increase his fasting and remembrance of Allah.