Applying cryptographic techniques in the field of 2D signal processing is an attractive approach in recent years. Different methods are proposed to ensure prior data protection. Symmetric block encryption schemes, designed on two-dimensional chaotic maps, are efficient and secure for real-time image encryption. In the case of numeric data, the encrypted information can be easily intercepted in order to be revealed. This creates a need to offer a posterior protection. In this paper a method combining chaotic encryption system with frequency watermarking is presented. The proposed technique is divided in two steps. In the first step, it consists in applying a modified Tao algorithm based chaotic map with higher complexity and applicable for all images sizes. The encrypted data is then hidden by coding it in the frequencies DCT coefficients of a transformed second image. The proposed approach presents more security and reliability for any kind of image data.