Tripcode

An imageboard or image board is a type of Internet forum which operates mostly via posting images. The first imageboards were created in Japan, and inspired the creation of a number of English language imageboards. They are based on the textboard concept.

Imageboards, similar to bulletin board systems, are used for discussions of a variety of topics. The primary focus of imageboards, however, is directed away from text posts, and is instead placed on picture posts. The two share many of the same structures, including separate forums for separate topics, as well as similar audiences. Imageboards are much more transitory with content—on some boards (especially highly trafficked ones), the thread deletion time can be as little as 10 minutes. In Japan, where imageboards are more common, topics will vary widely, ranging from trains to current news. The most popular English language imageboard, 4chan, similarly revolves around a wide variety of topics.

Imageboards are also different from online galleries in that most of the works posted are not made by the poster, but instead are taken from other online sources: galleries, other imageboards, and edited pictures.

Most imageboards and 2channel-style discussion boards allow (and encourage) anonymous posting and use a system of tripcodes instead of registration. A tripcode is the hashed result of a password that allows one's identity to be recognized without storing any data about users. Entering a particular password will let one "sign" one's posts with the tripcode generated from that password, while trying to take another user's tripcode and compute their password from it (for instance, to make posts that appear to come from a particular person) is computationally difficult. For those who want a custom tripcode, however, there are custom tripcode generators available, such as Meriken's Tripcode Engine and MTY_CL. In general, anonymity is considered to be one of the advantages of an imageboard, and some boards have from time to time removed the ability to post with a name altogether (known as "forced anonymous/anonymity").

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Wikipedia