What is the ruling on looking at a non-mahram woman?

Considering the fact that many women do not observe hijab properly, is unintentional look at them haram?

To what extent can a woman look at the body of a non-mahram man without lustful intentions?

Is it a sin to look at the photo of a painting which depicts an imaginary woman in nude?

In what circumstances it is not forbidden for a woman to shake hands with a non-mahram man? In order to pay allegiance, can a woman kiss the hand of a man covered with a piece of cloth?

What is the ruling on concluding a temporary marriage and having sexual intercourse with a non-Muslim girl who is not from the people of the book? Is there any way to make such relationship lawful?