We propose a practical method for the expeditious determination of the performance of imaging CCD and CMOS camera systems. special attention is paid to the operation of these devices in varying illumination conditions, which is typical to many surveillance and consumer electronics applications. One emerging application utilizing imaging sensors in variable illumination conditions is the third generation mobile phone, which will deliver wirelessly pictures, graphics, and video. In our method, determination of the system performance is based on the imaging of a calibrated gray scale test chart as a function of illuminance. At each level of illumination the system response is characterized by a signal to random noise figure. The signal is calculated as the difference of the system response to the lightest and darkest areas of the gray scale. The random noise is measured as the standard deviation of the gray values in a difference of two successive images of the test pattern. The proposed method is applied in three exemplary cases: 1. comparison of inexpensive CCD and CMOS cameras, 2. analysis of the effect of wireless image transmission, and 3. comparison of the effects of automatic and manual gain controls.