An image calibration method and device. A deviation compensation coefficient of each pixel is calculated according to image data generated by strong and weak lighting parameters, and the deviation compensation coefficient is used to calibrate data of each image pixel collected and output by an image sensing unit. Therefore, the influence of inconsistency of each photosensitive element of the image sensing unit on the image greyscale can be eliminated, so that the effect of document medium image recognition is increased. The method in the embodiments of the present invention comprises: S1, acquiring a strong lighting parameter of each photosensitive element within a long exposure time and a weak lighting parameter thereof within a short exposure time; S2, acquiring image data of a sheet medium; and S3, according to the strong lighting parameter, the weak lighting parameter and the image data, calculating the calibrated image data of the sheet medium.