An artifact is a residual image, shown on digital videos with poor resolution or poor light conditions.
The artefict occurs, when the camera's software miscalculates a certain area, and superimposes an even color on that particular area.
The artifact can resemple small boxes, small sculls, smileys and only the imagination is the limit!
Many ghost hunters interpret such artifacts as messages from the paranormal world. Or think the artifacts are paranormal phenomena themselves.
It is very easy to determine whether artifacts on a digital image are caused by the camera.