1. A method for setting an image monitoring area, which is implemented to an image monitoring device installed with an image processing software comprising a trigger parameter and a stop parameter the trigger parameter and stop parameter are included in an analysis procedure, for enabling the image monitoring device to utilize the image processing software to calculate and analyze a series of continuous image frames taken in a specific space by an image fetching unit and further including a calculation procedure, a record procedure and a set procedure comprising steps of: determining whether or not a target image in one of the image frames includes the trigger parameter including; running the calculation procedure to perform calculation with respect to the image frames and sending a result of the calculation to a memory unit for storage; running the analysis procedure to analyze the result of the calculation in order to determine whether the target image enters one of the image frames; when determining that the target image enters the image frame, running the analysis procedure to analyze the result of the calculation in order to determine whether the target image contains the trigger parameter; when determining that the target image contains the trigger parameter, automatically calculating, and analyzing subsequent image frames for procuring a trace of the target image, running the analysis procedure to analyze the trace of the target image moving in the image frames and recording the trace; running the record procedure to record the trace of the target image in the memory unit; determining whether or not the stop parameter is included in the target image in one of the subsequent image frames including; running the analysis procedure to analyze the result of the calculation in order to determine whether the target image contains the stop parameter; when determining that the target image contains the stop parameter in the subsequent image frame, running the set procedure to read the trace of the target image, stopping the recording of the trace of the target image and setting the area defined by the trace of the target image as the image monitoring area.