A Photogram does not have an original image to re-present as in photography, it becomes an image once a projection occurs, resulting in a unique shadow made by the variables of the light source and the intervening objects–-a material effect of the lucis interruptus.
Photogram is an odd name for the camera-less craft; while a photograph captures light onto a light-sensitive surface, a photogram relies on a shadow to make the image. The paper goes black under exposure, but the objects block the light, casting a shadow onto the paper, and that is the image you see. The places NOT exposed are the photogram. It should probably be called a Sciagram, or “shadow drawing”. Removing the lens from the equation fundamentally changes the projection paradigm. A lens transposes with such fidelity, we still see the apparent depth and other real-world information. In essence, it is a mirror–what you see is transposed to the film plane.
By distorting the paper surface into a modulating landscape, the projected light describes the surface articulation in varying degrees of shade and shadow. Light glancing along an edge of paper produces a lighter shade of gray than direct perpendicular contact. Developer is poured into the crumpled paper at varying heights, allowing time to seek level. The developing agents react to exposed areas leaving contour lines inscribed into the photosensitive landscape. The print is then dried and pressed, registering the former landscape in light.