Of all modes of producing photographs the photogram is the one most like the footprint in that it is the recording of an act of physical contact. Photograms are produced by quite a different method to traditional analogue photography. 

The photogram records the action of blocking light. What is attested to is the absence of the thing it depicts, not the thing itself. The photogram records an event, showing that an object, for a time, was in contact with the paper and protected it from the blackening effect of the light. The things recorded by a photogram have lived their way into the image. What is recorded is their act of resistance against the penetration of light.