Abstract: According to the effect of image capturing on image processing, a near-infrared source control system was designed for the hand vein image capturing system. The different assessment methods for the gray-scale images resulting from near-infrared imagery and their different applications were discussed, based on the information capacity, energy spectrum-entropy and false signal-to-noise ratio. A method was therefore proposed to assess the vein images quality, with which the relationship between image captured and light intensity was investigated so as to deduce the relationship between image quality and LED current, thus obtaining the optimal light source control/modulation signal. Applying the results of image quality assessment to light intensity control, a light source system was designed to integrate the near-infrared image capturing and image quality assessment with light source control together. As a result, the vein images meet the requirements of subsequent processing.