1. An image composition apparatus, comprising: an interface module, being configured to receive a plurality of images, wherein the images are aligned and are defined by a plurality of positions, each of the images comprises a pixel at each of the positions; a confidence analysis module, configured to calculate a confidence value for each pixel of each image; a sub-region extraction module, configured to suppress a portion of the positions according to the confidence values and determine a plurality of sub-regions for a composite image according to the unsuppressed positions; a source determination module, configured to determine a source for each of the sub-regions, wherein each of the sources is one of the images; and a sub-region growth module, configured to grow the sub-regions until the composite image is filled by the sub-regions, and configured to fill each of the sub-regions by the pixels in a corresponding sub-region of the corresponding source.