Hi I want to be able to detect cars or people or any object of interest in a live video. The camera will be far away from the target(ie the camera will be in a uav). How many pixels do i need on the target to detect the target ? You dont need to think about it from a uav point of view, the question is independent of that. How many pixels will i need on a car( 200 pixels, 1000 pixels ?), say for the histogram of oriented graidents, or haar classifiers or any object detection method to work reasonably well? If you can provide a reference as well, that will be preferred. Personal experience is fine as well.