A method for simultaneously capturing images of multiple areas is applied to an image processing device. The method includes scanning a document and obtaining a preview image of the document; providing N scan windows for selecting N to-be-scanned areas from the preview image, wherein N is an integer; setting N scan resolutions respectively for the N scan windows; scanning the document; and outputting N scan images corresponding to the N scan windows according to N frequencies of a timing signal corresponding to the N scan resolutions.