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For danbooru purposes a circle cut (サークルカット) is a special type of advertisement for a doujin circle. There are two basic types pictures tagged as circle cut. The traditional variety has some distinct features:
- They are (usually) in some standardized size, as specified by the doujin event;
- They are meant to be seen in monochrome, for the printed event catalog; however the circle cuts are usually in color for web catalogs;
- There is always a little, white, black bordered box in the upper left corner;
- The circle name is usually on the cut, as well as textual information about what the circle intends to offer.
The box is there for specific information, such as when the doujin circle will be attending an event and where their stand exactly is. See this image: http://yaplog.jp/cv/raitika/img/78/0_p.jpg for an example of a filled out circle cut. The box is also used by event goers as a checkbox, often with a highlighter.
The second kind picture doesn't need to conform to the visual template exactly, but is characterised by having been released as a direct preparation of the exposition in question. They might vary in appearance from just a character's portrait + circle name, up to entire small scenes or comics whose purpose is to announce the booth number. For example, see post #634255 and post #161515.