A unicorn chaser is an image or video of a unicorn which is viewed to cleanse the mind and the eyes after seeing unpleasant content on the Internet. The concept was pioneered by BoingBoing in August of 2003, when one of the editors posted a photograph of a mysterious rash and another editor followed with an image of a unicorn to push the rash down the page so that viewers saw the unicorn when they landed on the site, rather than a hideous rash. BoingBoing often includes unicorn chasers on their site after discussing unpleasant issues or displaying gross photographs, and some other websites have picked up the concept.
While it is certainly nice to view a pleasant image after looking at a disgusting image or a gross video, a unicorn chaser actually has several functions. On a major website, for example, the use of a unicorn chaser to bump posts down a page can ensure that visitors will not be disgusted when they navigate to a main page. It also allows people to view sites at work, since they can be confident that an unpleasant topic will not be the first thing to load. A unicorn chaser can also be used to showcase a found image on the web which the poster thinks that other people might enjoy.
A typical unicorn chaser is simply a picture of a unicorn, but variants include short videos with songs, or unicorns presented in a lolcat style, with silly, ungrammatical text. The style of art can be quite diverse; unicorn chasers may be altered photographs of horses, paintings, pastel drawings, or everything in between. It is also possible to use pictures of other fantasy creatures or baby animals in the same way that a unicorn chaser is used.
Classic situations in which a unicorn chaser might be used include postings of various unpleasant looking medical conditions, gross videos, or heated conversations and debates which get nasty. If you want to use a unicorn chaser on your own website, make sure that you have permission to use the image. Many artists are happy to have their images posted as long as you host them on your own servers and clearly credit the artist, but it is a good idea to ask first, just in case. You can also link to a unicorn chaser hosted on another site; BoingBoing, for example, has a plethora of past unicorn chasers in their archives.