1. A digital watermark information extracting method in which digital watermark information is extracted from image data which has the digital watermark information embedded therein by altering at least one pixel data located at a predetermined position on a specific coordinate and is geometrically deformed, comprising: an embedding position check step of performing the processing of extracting at least one pixel data at a predetermined position on the specific coordinate from the image data and comparing the data value of the pixel data thus extracted with a reference value to judge whether the information is embedded in the pixel data while applying the geometrical deformation on the image data until it is confirmed that the information is embedded in the pixel data; said embedding position check step comprising: a roughly checking step of executing the processing of extracting from the image data at least one pixel data located at a predetermined position on the specific coordinate and comparing the data value of the pixel data thus extracted with the reference value to judge whether the information is embedded in the pixel data concerned while the geometrical deformation is applied to the image data by every first geometrical deformation rate which is determined by a size of each of pixel blocks in which the alteration is made, a pitch of the pixel blocks and the number of the pixel blocks until it is confirmed that the information is embedded in the pixel data concerned; and a detailed checking step of executing the processing of extracting from the image data at least one pixel data located at a predetermined position on the specific coordinate and comparing the data value thus extracted with the reference value to judge whether the information is embedded in the pixel data concerned while the geometrical deformation is applied to the image data by every second geometrical deformation rate smaller than the first geometrical deformation rate within a predetermined range containing the geometrical deformation rate when it is confirmed in said roughly checking step that the information is embedded in the pixel data, until it is confirmed that the information is embedded in the pixel data concerned.