I buy gold

Photographs stand in special relation to time, for they describe only the present.
Exposures were long in early photography. If the subjects moved, its multiple image described also a space-time dimension. Perhaps it was such accidents that suggested the photographic study of the process of movement, and later, of the virtual forms produced by the continuity of movement in time.
Photographers found an inexhaustible subject in the isolation of a single segment of time. They photographed the horse in midstride, the fugitive expressions of the human face, the gestures of the hand and body, the bat meeting the ball, the milk drop splashing in the saucer of milk.
More subtle was the discovery of that segment of time that Cartier-Bresson called the decisive moment: decisive not because of the exterior event (the bat meeting the ball) but because in that moment the flux of changing forms and patterns was sensed to have achieved balance and clarity and order - because the image became, for an instant, a picture.
John Szarkowski

The photographer's eye