shunga ("spring drawing") is a style of erotic art dating back to the 12th century. Single paintings
s and books depicted couples having sex and (like most fine art, then and now) were available only to the wealthy upper class. Lavish "pillow book
s" were one of the items given to newly-married noble couples.
In the late 18th century, a lavish, flamboyant style of art called "ukiyo-e" was produced for rich nobles. As the less wealthy could not hope to afford such art, a market emerged for full-colour wood-block prints reproducing ukiyo paintings, as well as depicting popular actors and wrestlers, landscapes, animals and children.
For those who doubt that all new technology is immediately used for porn, I hasten to add that shunga woodblock prints quickly appeared. Though their sale was regulated, they were popular among commoners, and were produced openly up until the 19th century, when the form fell victim to more puritanical Western-influenced sexual mores (but continued illicitly).
In preparation to write this node, I perused a great number of shunga images available on the web. To my inexperienced eye (inexperienced, alas, to Eastern art, not pornography) these pictures are strikingly similar to modern popular erotica (aka "porn"). The couples are often in rather uncomfortable looking poses, apparently chosen to both approximate actual positions and wholly expose the genital area to the viewer. The male and female genitalia are lovingly depicted, in great detail. Penises seem to follow the larger=better philosophy. Unlike a lot of modern Japanese erotic drawing, female pubic hair was always depicted. Both the men and women seem to be greatly enjoying themselves, and though oral sex is not depicted (at least in the ones I viewed), masturbation (of the male and female) is commonly shown.
Sources: http://www.ptt.co.jp/tnl/ukiyoee1.htm, http://www.cwrl.utexas.edu/~pasupathi/critical_tools/e309k_spring_2000/archives/found/lib5/Shunga_the_Art_of_Love_in_Japan.html, http://www.thejapaneseconnection.com/Glossary/spring_pictures.htm
Those wishing to enjoy this erotic genre need only do a Google search for "shunga". If you're a real art historian, please add a more educated writeup here!