The digital signature approach offers an interesting alternative to classical watermarking techniques and is based on the idea of traditional paper- based signing by transforming it into the digital world. It consists mainly of extracting unique features from the image at the source side and encoding these features to form digital signatures. Afterwards signatures are used to verify the image integrity by signature comparison at the detection side. If any changes are made to the image after it was signed, they automatically invalidate the signature. Signatures as well as watermarks provide, among other qualities, protection from tampering, copyright infringement and illegal distribution. There are many methods to generate the signatures, for example, based on image histograms, colors, geometric information, frequency information, etc. The major drawbacks of digital signatures are similar to watermarks drawbacks. The main disadvantage is the need for a fully secure and trustworthy source. We need a common algorithm on both source and detection sides. The image alone is not self- sufficient to perform the authentication process. Because of this, the benefits of the active approach are significantly reduced.