>>472006171because photosensitive film, on which this photo was captured (ie those rolls that we used to put in cameras before we had digital ones), have an infinite resolution. well they dont really have any resolution. because there are no individual pixels.
even though the frame on the film is of a certain size (modern day film is 35mm big, which is obviously quite small), you can enlarge the photo to any size you want using an enlarger. basically light is shone through the film to a piece of photosensitive paper a distance away. because its a distance away, the image is enlarged. just like if you make a shadow puppet on the wall with your hand, the size of the shadow is bigger than your actual hand.