Objective To satisfy the discrimination condition of the glass packaging product in forming process by CCD and provide basis for its size measurement. Methods The monochrome irradiation response of the CCD to the glass packaging product and its surrounding scenery in different attenuation coefficient of the background light by the high temperature target radiation spectral power distribution theory and the Matlab numerical integration were studied. Results The functional relationship and curves between the gray difference between the high temperature glass packaging product and its surrounding scenery in CCD image and the attenuation coefficient of the background light were found. The gray difference increased as the attenuation coefficient decreased continuously and the critical value of the attenuation coefficient existed when the gray difference equaled zero. With the sunlight as an example, the relationship between the critical attenuation coefficient and the glass temperature was obtained and the critical value of the attenuation coefficient was 1. 6351 X10^-8 when the glass temperature was 900 K. Conclusion The discrimination condition of the gray difference greater than zero could be satisfied only when the attenuation coefficient of the background light was smaller than its critical value and the smaller the attenuation coefficient was, the better the discriminating effectiveness. It was presented that the method of decreasing background light intensity could be used to realize the discrimination of the glass packaging product in forming process by CCD.