Which of the following conditions would best increase film density in radiography?

The choice of having a shorter focal-film distance is correct for increasing film density in radiography. When the distance between the focal spot of the X-ray source and the film is decreased, the amount of radiation that reaches the film increases. This is due to the inverse square law, which states that as the distance from the radiation source increases, the intensity of radiation decreases. Thus, by shortening this distance, more X-ray photons will reach the film surface, resulting in a higher film density, or a darker image.

In contrast, increasing the distance to the X-ray source (as mentioned in another option) would lead to a decrease in film density due to reduced radiation intensity. Similarly, using a higher kVp setting typically increases the penetrating power of the X-rays, which can create more contrast, but it doesn't directly correlate with an increase in film density in the same manner that reducing the distance does. Reducing the film exposure time would decrease the amount of radiation the film is exposed to, further resulting in lower film density. Thus, it is the shorter focal-film distance that most effectively leads to increased film density in this context.