1. A method for decoding an encoded point matrix image including a first set of real grid points aligned along a first coordinate axis, a second set of real grid points aligned along a second coordinate axis that intersects the first coordinate axis, and a plurality of encoded data points distributed throughout the encoded point matrix image, the method comprising the steps of: (A) locating the first and second coordinate axes according to a first predetermined principle; (B) finding a set of virtual grid points according to a second predetermined principle, each of the virtual grid points being located at an intersection of a corresponding first virtual line parallel to the first coordinate axis and a corresponding second virtual line parallel to the second coordinate axis; and (C) decoding each of the encoded data points based on positional relation thereof with a closest one of the virtual grid points found in step (B) so as to obtain information encoded in the encoded point matrix image.