1. A foreground identification apparatus, comprising: a modest structure element (SE) determination module, for performing multi-scale opening by reconstruction (MSOR) and multi-scale closing by reconstruction (MSCR) operations, respectively, to an original image by using plural values of three-dimensional (3-D) structure element for determining a 3-D opening-by-reconstruction modest structure element and a 3-D modest closing-by-reconstruction structure element; an enhanced top-hat image and bottom-hat image generation module, for comparing the original image and an image obtained by performing MSOR operation with the 3-D opening-by-reconstruction modest structure element to the original image so as to generate an enhanced top-hat image, and comparing the original image and an image obtained by performing MSCR operation with the 3-D closing-by-reconstruction modest structure element to the original image so as to generate an enhanced bottom-hat image; a foreground identification screen generation module, for locating an overlap region between the enhanced top-hat image and the enhanced bottom-hat image, where the overlap region forms a foreground identification screen; a background mesh generation module, for simulating the variation of pixel colors in background areas extracted by the foreground identification screen for generating an interpolated background mesh; an image segmentation module, for dividing the original image into a plurality of regions and indexing the plural regions so that an image with indexed regions is obtained; a refinement module, for comparing the interpolated background mesh and the image with indexed regions for determining a refined foreground identification screen according to a refinement calculation; and a foreground identification module, for identifying and extracting foregrounds from the original image by utilizing the refined foreground identification screen.