What was a significant barrier to capturing fast-moving subjects like a running dog before modern photography?

The significant barrier to capturing fast-moving subjects, such as a running dog, before modern photography was the long exposure times required by early photographic techniques. In the early days of photography, the technology demanded that the camera shutter remain open for a considerable duration to allow sufficient light to reach the light-sensitive material. This typically resulted in blurry images when subjects moved quickly, as the motion would exceed the duration of the exposure time.

While the idea that fast-moving subjects could not be perceived by the human eye is intriguing, the actual challenge lay in the technology of the time, which was unable to freeze the action due to inadequate speed of shutter mechanisms and the slow responsiveness of photographic materials. Thus, the ability to capture sharp and clear images of fast-moving subjects did not become feasible until the development of faster film and shutter speeds in later years.