The rapid expansion of the Internet and the recent advance of digital technologies have sharply increased the availability of digital media. This paper is to investigate a wavelet based semi-fragile watermarking technique for image authentication. Image protection is achieved by the insertion of a secret wavelet tree based binary image signature (WTS) after wavelet decomposition followed by the quantization procedure. In addition, adaptive tuning steps are performed for the selected watermarked coefficients in order to increase the elasticity of watermark. During the verification, the original unmarked image is not needed for comparison. The detection of unauthorized tampering within the image is claimed by comparison with the possibly modified image's WTS and the authentic one.