An imageboard is a type of Internet forum that focuses on the posting of images, often alongside text and discussion. The first imageboards were created in Japan as an extension of the textboard concept. These sites later inspired the creation of a number of English-language imageboards.
Characteristics
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 has a large 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.
Tripcodes
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. 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 somewhat computationally difficult. For those who want a custom tripcode, however, there are custom tripcode generators (which are technically tripcode crackers) 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").
Secure tripcodes
Due to the fact tripcodes can be cracked given enough time, some imageboards, such as 4chan and 8chan, implement a "secure" tripcode. Such tripcodes are not reproducible across different imageboards; they work by prepending a secure salt to the tripcode, barring intrusion, known only to the server owner. They therefore function closer to a username than to a cryptographic signature; this is why QAnon could not verify themselves on another website when 8chan went down in late 2019.
Imageboards
2ch
Dvach, is a Russian imageboard that replaced 2ch.ru imageboard (originally known as dvach) which was shut down earlier on January 17, 2009; it thoroughly copied original layout and was heavily advertised over the internet and managed to succeed the original one in popularity. According to its owners number of posts left in the /b/ board exceeded 150 million. In September 2016 a pro-Russian government organisation, MAIL.RU, helped to organize "defense" against alleged DDOS attacks that took place during the same month; events raised concerns and speculations among users who grew suspicious over alleged takeover committed by the mail.ru and who criticized the owner's controversial decision to accept "help". As of October 2018 It was widely believed that imageboard was simply "sold" on undisclosed terms to pro-government organisation. The decision was met with high criticism of risks of disclosure of users' credentials in inherently anonymous-community to the government body that could potentially violate principles of anonymity, causing many to leave the board by the end of 2016. By 2019 it remains among the largest active Russian-speaking imageboards.
420chan
An English-language imageboard based on cannabis culture which was created on 20 April 2005 by Aubrey Cottle. The name is a reference to the larger 4chan and the code term 420 of the cannabis subculture. Its boards include various drug-specific boards, as well as a board featuring a chatbot named Netjester.
4chan
4chan is an English-language imageboard based on the Japanese imageboard Futaba Channel. This imageboard is based primarily upon the posting of pictures (generally related to a wide variety of topics, from video games and popular culture to politics and sports) and their discussion. The Guardian describes it as "at once brilliant, ridiculous and alarming."