i saw it when i was like 10 in 2009 (if i remember it looked like an early 2000s drawing)and i remember it being one of the first things to always show up whenever you look up something basic like "anime gore drawing" it was a picture of a schoolgirl that smashed another school girls head into a wall. if i remember correctly they wore blue uniforms, the killer girl had a crazy smile on her face and looked directly at you and the dead girls head was smashed sideways so one half of her face was visible the other part was either in the wall or exploded. the wall was grey and had cracks around her head. artstyle is similar to this pic i think.