A method for monitoring a field of view for visible changes is disclosed. A first image is taken in a predetermined manner of the field of view to be monitored, and then an array divides the first image into a plurality of cells. A second image is taken in the predetermined manner of the field of view to be monitored. The array is also applied to the second image, dividing the second image into the plurality of cells. Predetermined groups of cells of the second image are then compared to the same groups of cells of the first image, and the number of the groups of cells that changed from the first image to the second image is computed. In some situations only certain groups of cells are compared. In one form of the method, each cell of the first image is given a numerical value based upon the information in each cell, and each cell of the second image is also given a numerical value based upon the information in each cell. Each group of cells is also given a numerical value based on the numerical value of the cells within the group, such as the sum of the numerical values of the cells within the group. In one arrangement, each cell is a single picture element, known as a pixel. The numerical value of each group of cells is the sum of the brightness for the pixels in the group. In one such arrangement, the predetermined groups of cells comprises a single group. In one method, the number of the groups of cells which changed in numerical value by more than a predetermined amount is also computed.