Xie and Shen  improved Barni's basic pixelwise masking model and proposed a more robust wavelet-based watermarking algorithm against attacks including filtering, noise addition and compression. By extending their work, a new robustfragile double image watermarking algorithm is presented. Using the improved pixel-wise masking model and a new bit substitution based on pseudo-random sequence, our method embeds robust watermark and fragile watermark into the insensitive (robust) part and sensitive part of the wavelet coefficients of the host image respectively. This makes the two watermarks non-interfering and increases the watermarking capacity of the host image without reducing watermark robustness. Experimental results validated these desirable properties of the proposed method, and showed that our method has a higher PSNR than the existing double image watermarking schemes ,  while retaining the same robustness as the sigle watermarking scheme .