Abstract: The present invention relates to a digital image watermarking apparatus and method. Luminance component of a digital image are transformed into coefficients of a frequency domain, and watermark is generated by encrypting a user key and generating pseudo random number from encrypted user key. Then, a replacement coefficient generated from a coefficient of a first frequency area and the watermark is replaced with a coefficient of a second frequency area so that the watermark is embedded into the digital image. The embedded watermark is extracted at an authenticating apparatus and the digital image is authenticated by finding the correlation between the extracted watermark and watermark for authentication.

Abstract: A method for embedding and detecting watermark by a quantization of a characteristic value of a signal is disclosed. In order to embed watermark, first, a signal which will be watermarked is segmented in a predetermined time period, and a characteristic value with regard to a signal within the frame obtained therefrom is evaluated in a predetermined manner. Quantized values within a set corresponding to a value of pattern information embedded into the frame among a plurality of sets including one or more quantized value respectively is compared with each characteristic value so as to determine a quantized value closest to the characteristic value. The intensity of insertion used for modifying the signal within the frame in order to make the characteristic value same as the determined quantized value is evaluated, and the signal within the frame is modified based on the evaluated intensity of insertion. The watermark detection is performed in a similar process as the embedment.

Abstract: The present invention relates to a method for embedding a watermark into a black and white or color digital image [D(x)]. Basically the inventive method comprises the steps of transforming the digital image using a wavelet transform [WC(y)], transforming a watermark using discrete cosine transform (DCT), integrating the wavelet-transformed digital image with the DCT-transformed watermark [DW(x)+WC(y)] to insert the watermark into the image, and generating the watermarked image using inverse wavelet transform [D(x)?]. For color images, RGB mode is converted into YIQ mode using a conversion matrix and the wavelet transform is applied to the Y-, I-, Q-values. This inventive digital watermarking of a color image is found to be highly robust against lossy compression and other image processing operations, compared to conventionally known methods which are known to be unsuitable for watermarking color images.

Abstract: The present invention relates to a method and apparatus for authenticating various types of digital certificates by using a text embedding method. The execution of the present invention is divided into two case, one case including images in the certificate and another case not including the images in the certificate, according to the characteristics of the certificate. In the former case, a text embedding method is applied to images included in the certificate to embed a series of information text (a specific number of the certificate, and issuing organization, name of a person in charge, etc.) designated by a person who issues the certificate into the images. In the latter case, there is generated an image imperceptible to the human eve but having the same color as the ground color certificate.

Abstract: Digital watermarking of digital audio is performed by Fourier transforming digital audio data, wavelet transforming the magnitude components of the Fourier transform coefficients of the digital audio data, discrete cosine transforming a watermark signal, multiplying the sign of the wavelet transform coefficients of the magnitude components to the coefficients of the discrete cosine transformed watermark signal, adding the coefficients of the Fourier transformed digital audio data and the adjusted discrete cosine transformed watermark signal, and inverse wavelet transforming the audio signal's coefficients before inverse Fourier transformation to finally generate watermark-embedded audio signal data.