A digital watermark is a signal that is embedded into digital data (text, image, audio, video) in a manner that allows it to be extracted later. This is done by embedding a pattern which contains the author's data into the digital data. In this research, we propose a comparison between three types of transformations for embedding a watermark in the frequency domain into digital images in an efficient and secure method that allows the watermarking any type of digital images with good perceptibility.