A method for the prior monitoring of the detectability of a watermarking signal inserted by modulation in a set of coefficients representing for example a digital image. The method comprises the step of simulating a distortion on the set of modulated coefficients, the distortion corresponding to a given compression level of the set of coefficients before modulation, determined by optimisation of a ratio of transmission rate to distortion. The method further comprises the step of calculating a detectability test on the set of modulated coefficients after distortion, and a step of comparing the detectability test with a threshold detection value. The method is used notably for inserting a watermarking signal during the compression of a digital image.