This Masters thesis describes the process of implementing a semi-fragile watermark, examining especially the usage of the wavelet transform as well as the creation of pseudo random numbers to enable secure encryption and embedding of a watermark. Based on the realized application, experiments with different sorts of image manipulations were conducted to demonstrate its robustness and ability to authenticate the embedded watermark. In this context it could be discovered that particularly the wrong usage of pseudo random number generators failed to securely encode a watermark, as the created sequence of numbers did not show sufficently random behaviour. In terms of usability, an efficient implementation of the wavelet transform could be proved inevitable. Here, selecting an appropriate color component, while embedding a watermark, has a significant impact on invisibility and color accuracy.