A method for real-time adjusting image capture frequency by an image detection apparatus comprises: sensing the frames consecutively by an image detection unit; setting a value for a counting variable; selecting a testing frame from the frames and comparing an image displacement between the testing frame and a previous frame thereof, to obtain a motion reference signal by a processing unit; providing a plurality of adjustable values for a capturing frequency variable by a memory unit and corresponding either one of the capturing frequency variable values to the motion reference signal; comparing the value of the counting variable to that of the capturing frequency variable by the processing unit; capturing and recording the testing frame as a sampling frame while the counting variable value reaches that of the capturing frequency variable; comparing an image displacement between the sampling frame and a previous frame thereof, to obtain an ultimate motion speed.