A method of locating and decoding a two-dimensional machine-readable symbol in a digital image, where the symbol has three finder patterns adjacent respective corners of the symbol, takes into account the possibility of skew and pitch when delineating the symbol in the digital image by estimating the unknown fourth corner based on lines passing through known symbol edge points. On the basis of the delineating, a reference grid is mapped to the digital image and a bit stream is extracted based on the mapping.