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Fragile watermarking methods have been widely used for image authentication. In order to increase the fragility of digital watermarking techniques, cryptologic hash functions, parity bits and secret sharing methods are generally used. In this article, a new image authentication method based on singular value decomposition (SVD) with a new block-based data hiding technique is proposed. The block size can be determined by the user in the proposed method. In this work, 2 × 2, 4 × 4, 8 × 8 or M × M size of blocks are used. Features are e×tracted from each block using SVD. E×tracted features are quantizated by block size. In the stage of watermark generation, watermarks are generated by using secure pseudo random generators. The generated watermark is encrypted by e×tracted features and encrypted watermark is embedded into cover image using the proposed data hiding function. This method consists of preprocessing, feature e×traction, quantization, watermark generation, watermark encryptiom, watermark embedding, watermark e×traction, watermark decryption and tamper detection. The visual quality of the suggested method is measured by peak signal to noise ratio (PSNR) and tamper detection capability is measured by bit error rate (BER). E×perimental results have demonstrated that the proposed method is successful. [ABSTRACT FROM AUTHOR]

Compressive Sensing (CS), which makes it possible to reduce the amount of data and thereby to greatly simplify the sensor system has become a very important research area. In this method, data is compressed before measurements whereas data is first measured and then compressed in the current technology. This approach leads to reducing the number of sensors. In this study, simultaneous compressive sensing and hybrid optical cryptography is developed as a new approach to handle two important problems in the field of communications, namely, effective and efficient signal processing and secure transmission of information. In this work, CS is achieved with the orthogonal matching pursuit (OMP) algorithm. Then, the CS-OMP algorithm is combined with the double random phase encyrption (DRPE) method to achieve both compression and encyrption of data. In order to achieve high security, the keys used in CS and DRPE are transmitted to the receiver by an asymmetric cryptography method. Thus, the overall cryptographic system is a hybrid optical system (both symmetric and asymmetric) since DRPE is a symmetric optical encyrption method. [ABSTRACT FROM AUTHOR]