This paper presents a new proposal for the insertion and extraction of watermark into digital images based on the wavelet transform. The insertion of the watermark is perfomed in a high frequency sub-band, containing the horizontal detail coefficients of the host image, decomposed once by the twodimensional discrete wavelet transform. This sub-band is once more decomposed before inserting the watermark. The encryption process includes the division of the watermark in blocks, an encoding algorithm, exchanging positions of elements and random allocation of the blocks at the time of its inclusion in the sub-band chosen. The robustness of the method is verified by applying three very common attacks in images with watermarks, noise addition, lossy compression and JPEG compression.