The invention relates to the technical field of image processing and particularly discloses an image processing device, an image processing system, a video capture card, a display device, and a set-top box. The image processing device comprises a signal input interface for receiving originally input image signals, an image adjusting module, a backlight adjusting module and a signal output interface. The image adjusting module is connected with the signal input interface and used for adjusting contrast of the image signal so as to improve the contrast. The backlight adjusting module is connected with the image adjusting module and used for calculating a backlight dimming signal according to the adjusted contrast. The signal output interface is connected with the image adjusting module and the backlight adjusting module and used for outputting the adjusted image signal and the backlight dimming signal. By the signal input interface and the signal output interface, interface input/output of different signal formats is adopted according to different applications, universality and expansibility of the image processing device are improved, and energy conservation of the display device for displaying images is achieved.