In this paper, we present a new semi-blind watermarking method with secret key by embedding several watermarks in the same image. This embedding is done when the originale image is being coded by the Embedded Zerotree Wavelet (EZW) coder, a compression method based on the wavelets transform, proposed by Shapiro in 1993. Therefore, the detection processus is performed at the time of decoding the compressed watermarked image. Our algorithm, tested on several greyscale images of size 256 x 256 and for several compression rates, staies robust to intentional or unintentional image processing operation as long as the compressed watermarked image is stilling exploitable exploitable.