25. The system of claim 20 , wherein the feature indexing unit creates a quantization tree and adds a feature point to the quantization tree for the invisible junction feature descriptors.
25. The system of claim 20 , wherein the feature indexing unit creates a quantization tree and adds a feature point to the quantization tree for the invisible junction feature descriptors. 26. The system of claim 25 , wherein the feature indexing unit adds the feature point by adding a leaf node including a page ID and coordinates (x, y) of the feature point.