1. A protection method for preventing a hard copy of a document from being released or reproduced, the protection method comprising: selecting an image comprising a background and at least an object having a closed boundary; pre-processing the image to generate a pattern having a closed contour line; utilizing a level set method to process the pattern to generate at least a watermark; and embedding the watermark into the document; dividing the hard copy of the document into a plurality of blocks, each of the blocks having a plurality of pixels; detecting the hard copy of the document to determine whether the watermark exists in the hard copy of the document; and forbidding scanning or copying the document when the watermark is detected in the document; wherein the step of detecting the hard copy of the document to determine whether the watermark exists in the hard copy of the document comprises: setting a watermark block number threshold; determining a watermark block number of the hard copy of the document according to a color duration characteristic of the pixels in each of the blocks; comparing the watermark block number with the watermark block number threshold to generate a comparing result; and determining whether the watermark exists in the hard copy of the document according to the comparing result wherein the step of determining the watermark block number of the hard copy of the document comprises: utilizing a multi-directional texture searching algorithm to determine if the color duration characteristic of the pixels in each of the blocks meets a color duration characteristic of the watermark, wherein a block is considered as a watermark block when a color duration characteristic of the pixels in the block meets the color duration characteristic of the watermark; and counting watermark blocks to determine the watermark block number of the hard copy of the document.