A method of capturing an image of a document is provided. First, a notebook computer having a base is provided, wherein an image pickup device is disposed on the notebook computer, and a symbol mark is formed on the base of the notebook computer. Next, a document fixer having a fixer middle mark is provided. The document is fixed by the document fixer, wherein a centerline of a long edge of the document is aligned with the fixer middle mark. Next, the document fixer is moved according to a size of the document until the fixer middle mark is aligned with the symbol mark. After the image of the document is captured, an image processing procedure is performed. By aligning the fixer middle mark with the symbol mark of the notebook computer, the document is precisely positioned and thus a sharp image with no tilted distortion is acquired.