1. A face recognition system implemented on an image capturing device for taking group photos, comprising: a face recognition module, to read and obtain one preview image of a group photo and recognize complete faces in the preview image; a dividing module, to divide the preview image into a plurality of default blocks when the number of the complete faces is more than or equal to a predetermined number; a block adjustment module, to adjust the default blocks into a plurality of adjusted blocks, the adjusted blocks comprising a number of complete face blocks and a number of non-complete face blocks, wherein each of the complete face blocks contains only one complete face while each of the non-complete face blocks does not contain any complete face, and one of the most adjacent complete face blocks contains one of the most adjacent complete faces; an analysis module, to analyze the adjusted blocks to obtain a plurality of target blocks from the non-complete face blocks which is most adjacent to any one of the blocks which comprise the complete face; and a feature recognition module, to recognize facial features in each of the target blocks and obtain a plurality of non-complete face blocks, each of which comprises any of the facial features.