This paper presents an algorithm of digital image watermarking that uses a text as mark. Our proposal generates an optimal level of robustness according to the parameters considered for watermarking. The proposed algorithm consists in the insertion over an image of a text string, previously modified by permutation using a random key and an OVSF (Orthogonal Variable Spreading Factor) generator. The insertion is made in the wavelet domain and uses Quantization Index Modulation (QIM). Also, the conditions to reverse the process and restore the original information are set. Finally, the robustness of the proposed algorithm is evaluated implementing several attacks on the marked image.