Official art created by a guest artist. Either commissioned by a copyright holder or is gifted to the author of the work by other established artist.
This is often seen in the end matter for published manga or books (e.g. alongside the work's primary artist's afterword), or featured in end cards or eyecatches in animated works, or in specially produced extra content, officially sanctioned promotional art, and the like.
Don't use this tag for images posted in collaborative works where no one artist dominates the artwork, even if one artist officially edits and publishes the work and/or solicits work from other artists.
