I see images like these post #7939317 post #7995674 post #7772464 from time to time - thick black border, white square in the corner - and I never know what they are or what it means. I see them from time to time from different artists, and they seem to be showing up around Comiket, but I don't have even a guess of what it could be. Does anyone know?
Updated by Unbreakable