This article presents a new approach in the selection of auspicious sites to be watermarked. The selection takes into account human visual system properties including luminance adaptation, contrast sensitivity and spatio-frequential selectivity. This article exploits also the local band limited contrast to determine the maximum watermark strength to be applied without inducing visible degradations. Compared to the well-known approaches, a contrast masking model is used here to adjust, site by site, the watermark strength. To test the approach efficiency, obtained results are considered in the context of an adaptive watermarking algorithm. The performance of this latter is evaluated in terms of watermark invisibility and robustness. Watermark invisibility is judged through subjective tests conducted with three observers according to the CCIR recommendations. Original watermark detection results are also presented to analyze the robustness of the scheme to most common attacks such as JPEG compression, cropping (with zero padding) and blur.