The blurred images will make image processing difficult and be hard to get high image solution for recognition, which will lower the precision of a variable rate spray system in pesticide application. In this paper, Radon transform in frequency domain is used in this work to test the blur angle and blur length in different tractors speeds and camera heights. Four image restoration methods in terms of the shape, color, texture and computing time were compared. The results showed that the speed of tractor and the height of camera played an important role on the blur extent of real-time image. A mathematical model corresponding blur angle and blur length with the speed of tractor and the height of camera is established, which would provide a theoretical basis for reducing blur and improving the quality of real-time image.