Digital watermarks have been proposed in recent literature as a method for copyright protection of multimedia data. Digital watermark is invisible mark embedded in digital image, video or audio documents, by detecting the information of watermarking to protect copyright of multimedia data. Most published watermarking methods are based on two-dimensional (e.g., image or video) approaches. A new algorithm of digital watermarking in three-dimensional (3-D) space based on the methodology of virtualoptics is presented. The watermarking algorithm can offer an effective solution to the issue of copyright protection of multimedia data. Numerical experiments show that the embedded watermark is robust to signal manipulations, such as superposing noise, cropping and lossy compression. Because the concept of virtualoptics is introduced, the proposed scheme has good security. There are large degrees of freedom existed for designing a security lock(s)/key(s), including multiple lock(s)/key(s) and multi-dimensional lock(s)/key(s). Numerical simulation results show a good agreement with theoretical prediction.