What should one do if they find pictures of unveiled women in a commercial establishment, and they do not know the owner to inform him of the impermissibility of that?

If there are open transgressions in the place, it is your duty to denounce them to its owner and those who act on his behalf, to the best of your ability, based on the saying of the Messenger of Allah, peace and blessings be upon him: "Whoever among you sees an evil, let him change it with his hand; if he is unable to do so, then with his tongue; and if he is unable to do so, then with his heart—and that is the weakest of faith."