regular color

converted to gray

vertical trace

horizontal trace

horizontal and vertical trace

2 color image

difference image
effect is a trace of moving objects/people
behind their movement appears the background

shadow
effect is a movement/moment is captured and stays even if the object has moved away
if an object stays motionless in the picture it will disappear and reappear with the movement  

all effects combined

Ebru Ozsecen
Niels Thorwirth
Florian Altmann