No matter which kind of sensoric proceeding or measurement methods you have, you will always come necessarily to a certain limit of resolution. This is a result of the principles of measurement and the processing of signals right up to sampling theorem. This also concerns area sensors, such as video sensors.
In consequence of the prevalent environmental conditions, the quality and the focal distance (zoom) of the objectives, the character of the sensor etc., every setting has its own specific limits of resolution. For that reason the success of a measuring system is to consider this limits. That is why planning a system has to start with the exact describing of the scope, then to choose the ideal technic and finally doing the sizing of the project (dimensioning) considering all this informations.