1. A portable computer system for capturing a target image related to an item, comprising: a base; a cover pivotally connected to the base, the cover comprising a panel projecting the light onto the base and rotating according to a size of the item; an image capturing module being pivotally connected to the cover and comprising a calibrator, the size of the item corresponds to the calibrator, the image capturing module rotating with respect to the cover to capture a reference image according to the size of the item; and a lightness adjusting module, for adjusting the lightness of the panel according to the reference image; wherein the image capturing module captures the target image related to the item after the lightness of the panel is adjusted.