You should never pressurise anyone into making an explicit image. It is against the law to take or hold an explicit image of someone under the age of 18.
Source: Sexting: What parents need to know @ http://www.bbc.co.uk/webwise/0/25859561
image: Pro Juventute Aufklärungskampagne ‚Sexting’ Themenbild_10 by Pro Juventute under Creative Commons license