1. A pattern recognition method applicable to a single image file including a plurality of regions, the method comprising: obtaining certainties in which each region of the single image file includes a respective one of a plural of human face patterns by a first face detector; determining a certainty distribution of the certainties obtained by the first face detector; determining dynamically a threshold certainty based on the determined certainty distribution; selecting at least one combination of the region and the human face pattern, the selected combination corresponding to the certainties which are equal to or greater than the determined threshold certainty; and detecting at least one human face image based on the selected combination by a second face detector.