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This paper presents a novel method named as Modified Orthogonal Search Algorithm (MOSA) for the block based motion estimation. Recently fast search algorithm for video coding using Orthogonal Logarithmic Search Algorithm (OSA) has been proposed by Soongsathitanon et al. (IEEE Trans Consum Electron 51(2):552-559, 2005).We introduce the center biased search point pattern for the estimation of small motions and a half way stop technique to reduce the computational complexity in the existing OSA. This feature improves the speed performance of the algorithm by 80% as compared to the Full Search Algorithm, 50% over the Three Step Search algorithm and 2% faster than the OSA. However, the Mean Square Error and Signal to Noise Ratio did not show significant deviation from the orthogonal logarithmic search algorithm and the three step search algorithm. The experimental results based on the number of video sequences were presented to demonstrate the advantages of proposed motion estimation technique.

For image authentication, the competence of accurately locating tampering and ensuring security is desirable. In this paper, a novel reversible data embedding based on Integer Wavelet Transform for tamper-proof watermarks is proposed. A content-based watermark generated from host image is embedded into the carrier. The embedded data can be retrieved and the original host image can be recovered without distortion. The difference between the extracted watermark and the watermark generated from specific coefficients representing local features is applied to localize tampers. Experimental results show that the host image can be recovered after extracting the watermark if there are no attacks. Otherwise, the tampered positions can be localized explicitly and directly in the reconstructed host image even if the watermarked image was attacked by an invisible tampering. The proposed algorithm can be used for image authentication and tampering localization without using original image and original watermark.

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