Some visual ITC methods rely on creating a shifting physical scene that can be observed directly, with a camera used only to document what happens. One of the simplest involves using fine water vapour - often from a smoke machine or similar device - drifting through a thin bar of visible light. The vapour naturally curls, rolls and breaks apart, forming constantly changing shapes within the illuminated area.

Because the movement is unpredictable, the patterns can sometimes resemble outlines, faces or silhouettes. Some investigators believe that spirits might be able to influence these shapes.

The effect relies on producing a narrow bar or sheet of visible light rather than a broad beam. This can be created using a slit or narrow gap, or by masking a light source so that only a thin strip escapes. When vapour drifts through this strip of illumination in an otherwise dark environment, only the parts of...