In high-power lasers, nonlinear hot image is likely to damage expensive optical components. The damage risk of hot image to optical components may be reduced by identifying and eliminating the obscurations which induce the most intense hot images. The relationship between intensity of nonlinear hot image and dimensions of obscurations has been investigated theoretically and numerically. According to the theory of propagation of light spectrum and the Bespalov-Talanov theory, an expression for intensity of hot image through thick nonlinear medium is derived; the relationship between intensity of hot images and dimensions of obscurations is investigated and verified by numerical simulation. It is shown that, the bigger the obscuration is, the more intense the hot image is, when obscurations reach a certain size which is approximately determined by the fastest growing spatial frequency of the Bespalov-Talanov theory, the hot image becomes the most intense one, for a bigger obscuration, the intensity of its hot image decreases.