Confusions regarding frame rate?
In this case, images/frames are moving horizontally or vertically?


Neither. They just appear; usually, they stand still for as long as a frame is displayed.


  But what is the minimum rate of frame/images so that still images appear as video?


That depends on a lot of factors like brightness, amount of motion in the material, and mental state of the observer.

Typically, upwards of roughly 20 frames a second, things are perceived as fluid motion, but there seems to be some benefits to going higher in frame rate, especially in high-movement scenes.

Traditionally, cinema and TV used to be 24 or 25 frames a second, but this number has changed in recent years, with digital TV producing whatever frame rate the video codec used does.