If a person sitting across to a girl in public transport deliberately shows a pornographic picture to her, it amounts to the offence of

Showing pornographic material to a woman without her consent constitutes sexual harassment under Section 354A(1)(iv) IPC. The act is specifically listed - 'shows pornography against the will of a woman'. It is not voyeurism (which involves capturing private images), not sexual assault (which requires physical contact), and not 'none of these'.