1. An image-based technique for shredded document reconstruction, comprising the steps of: a) Image processing where shred images for reconstruction are acquired by scanning the shredded document, and then the image of the shred in each shred image is discriminated from the image of the background, and then the non-text region of white background color and the text region of black text block are separated by segmenting the histogram obtained from the horizontal projection of each shred image; b) Special Shred Selection where the shred images are classified, so that the blank shreds, the leftmost shreds containing the text part of the original document, and the rightmost shreds containing the text part of the original document are selected; c) Shred Coding where the base-lines of the text lines of the shred images are united into a group, and then the midpoint coordinates of the projection histogram of the base-lines of one same text line is served as the vertical coordinates of the respective text line, and then a shred model is created from all of the shred images by uniting the vertical coordinates of the text lines, and then a binary coding is followed for the individual shreds so that each shred image has a corresponding shred code; d) Similarity Measure where a predetermined algorithm is employed to calculate the binary codes of the shreds, thereby obtaining a correlation score for the binary code of each of the shreds; and e) Sorting Scheme where the shred images are sorted based on a graph architecture by using multiple vertices to represent the binary codes of the shreds and multiple edges to represent the correlation scores between the pairs of the shred images and then employing a contraction operation on the vertices and the edges; thereafter a first stage sorting is employed by: sorting the order of the shred images, which order being the order of different shred codes; thereafter, a secondary stage sorting is employed on the shred images having one same shred code to get the order of the shred images having one same shred code; thereafter the first stage sorting result and the second stage sorting result are combined together to obtain a complete image, achieving shredded document reconstruction.