![2girls ahoge bible bikini_bible_chan black_hair blonde_hair blood blood_on_face blue_eyes bone book brain breasts censored cross large_breasts mitre monster_girl multiple_girls nipple_censor original panties paul_robertson pixel_art red_eyes school_uniform thong underwear zombie rating:q score:2 post #152975](/cdn_image/preview/77/98/77986c3b1ae0f8ac3110d413bd3bee7c.jpg)
This tag indicates that an image exhibits a distictive pixelized style (e.g. jagged edges, dithering). This may be either intentional or as a restriction on the software used to render it. This is common in older GIF images as well as images meant to invoke game sprites.
Pixel art is almost necessarily digital art in a rasterized format, and as such is naturally mutually exclusive with traditional media and vector traces.
Different from oekaki which is a very specific concept.