US Patent 7116824 Detection of a pattern in a digital image

A method for detecting a pattern in a digital image by successive comparison of the content of current windows with the content of at least one reference window representative of the pattern, the reference window containing values of variance or standard deviation of sub-blocks of pixels of the pattern and the current windows containing values of variance or standard deviation of sub-blocks of pixels of the image, the sub-blocks being of the same size in the current and reference windows.