While a motion picture is actually made up of a series of still images, what actually works for a moving image is very different than for a still one.  In fact, the two could not be more different, despite the common misconception that a production’s publicity campaign borrows actual frames or “screen captures” from the film itself. 

In general, a blowup or screen capture taken from a frame of a motion picture is not of necessary quality for print publication. This is because a still image has far greater resolution and overall image quality than its motion picture counterpart.

As illustrated above, a 35mm motion picture frame (such as Super 35 as used in the Matrix Trilogy) does not use the same familiar 24x36mm as used in 35mm still photography.  This is due to the different aspect ratios involved,  the fact that most motion picture cameras expose film vertically, not horizontally, and other factors.  Whether a computer generated image (CGI) composite, or a scan from the actual film itself, motion pictures simply do not need the same resolution, and as such - are orders of magnitude smaller.

In addition, a still frame is often exposed at shutter speeds some 4x faster or more to freeze the action ordinarily blurred by a motion picture camera. Aided by retention of vision, a series of blurred motion picture images will appear sharp to the viewer, even though each actual frame (within the series) is not. 

Moreover, the viewing conditions of each respective format are entirely opposite. While a motion picture is often projected in a darkened auditorium, viewed by the public many feet away, still photographs are studied carefully in bright lighting, only inches away, whether in a photography gallery or newsstand. 

Finally,  35mm image quality aside,  today’s digital still cameras (such as the Canon 1ds series, Nikon D2x , or Kodak slr/n) now offer medium format quality resolution  - more than 4x higher than 35mm,  suitable for high end applications like posters or print advertising. And, because today’s professional digital still cameras need only capture a single image at a time, they are currently way ahead of their digital counterparts in the motion picture world. Digital Video cameras (DV) cameras would quite literally require over 20x the resolution per second to match a single digital still. 

In short, the technical demands of a still image dictate a very different standard  to be considered of the same quality as a series of moving pictures.  What works for moving pictures simply does not for still ones.  As such, film productions utilize the special skills of a Unit Stills Photographer, often one of the sole crew members intent on expressly creating still images for the production.