The article discusses semi-fragile digital watermarking systems designed to protect JPEG images against unauthorized changes. These systems allow detecting and locating changes, and some of them are able to restore the original content. Formal schemes describing the procedures for watermark embedding and authentication are given. We consider more than a dozen systems of this type and classify them according to various criteria. We also consider the results of experimental studies of these systems estimating their level of distortions arising from watermark embedding. In addition, we test the systems whether they are able to operate in the semi-fragile wayю

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