Exhibitionism used in its psychiatric sense means that a person likes others to see his (rarely her) sexual parts or likes other people to see him/her doing sexual things.
Voyeurism means that a person likes looking at the sexual parts of other people or likes to watch other people doing sexual things.
5:28 But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart.  and some Christians interpret that as meaning that a man can’t even look at his own wife that way.  A Christian man can’t ever look at pussy, he can’t even look at his own wife’s (...) Can a Christian woman look at her husband’s *****? The Bible is less clear there so different fundy Christians probably disagree. Fundy Christians hardly ever give women more freedom than men so a good Christian wife should probably look modestly away when her husband comes to her undressed.
(Perhaps Jesus was not so keen on sex, perhaps Jesus was more touchie feelie with Mary Magdalene.) Due to this over the centuries goodly Christians felt their duty was to avoid looking at their wives or husbands that way and even sometimes today that happens. So good married Christians used darkened bedrooms other places were just a little improper, they avoided mirrors, never undressed together and did everything between the sheets in the missionary position spoiling half the fun.
Consensual exhibitionism and consensual voyeurism are not a problem except for sexually repressed Conservatives. In gay bath houses leaving a door ajar but not fully open can be a signal that others are welcome to watch but not to join in.
Non consensual acts of Exhibitionism and voyeurism can be distressing for other people who don’t want to see something sexual or don’t want to be watched when they are doing something private and such Non consensual acts are commonly illegal in many democratic countries.
Many Kids and adults like to send sexy pictures of themselves through the Internet. Middle aged elected representatives do it though they should be sensible enough to understand the risks. Even a UK Member of Parliament, thought he could trust a woman he knew only online but "she" was a male undercover reporter and betrayed him. Also pictures 2 women posted online were used without the women's consent to trap the MP. 
During flirtatious chats and photo exchanges, [the MP] sent a graphic snap exposing himself while wearing a pair of paisley pyjamas. After the undercover reporter sent him an explicit picture supposedly of “Sophie”, [the MP] asked for a more explicit picture “without your hands in the way and legs parted”. The MP overlooked how unreliable and unforgiving the Internet can be. Very young kids below 16 also send photos of themselves online. Later they likely wish they hadn't done it because the people who get the pictures sometimes betray the kids, threaten to tell their parents and other nasty stuff. That can even lead to Suicide.  Police in the UK are refining their systems to trap those who get photos from underage kids.  and people who take advantage of kids that way in other nations are also prosecuted.
People get or give each other sexy pictures during a relationship, then if the relationship goes sour their partner gets revenge publishing humiliating pictures. Organised criminal gangs blackmail people over sexy material sent online, this can involve pressuring victims to hand over Money, to take part in hard core pornography or to do sex they don't want. 
Never trust anyone you know only online, someone who seems Cool and likable online can in reality be an evil criminal wanting to take advantage of you. If anyone is using pictures of you to blackmail you go to the police.
- ↑ http://skepticsannotatedbible.com/mt/5.html#28
- ↑ http://www.ewtn.com/library/papaldoc/jp2tb42.htm
- ↑ Brooks Newmark quits: MP says he is 'battling demons'
- ↑ Brooks Newmark Quits As MP: 'Sexting' Scandal Places 'Intolerable Burden' On Family
- ↑ Disgraced Tory Brooks Newmark caught in new scandal and will quit as MP
- ↑ Child sexting cases 'reported daily' in UK
- ↑ Child abuse database containing millions of images to launch
- ↑ Police warn men over online 'sextortion'
Adapted from RationalWiki