1. Method of determining a segmentation into distinct regions of a set of coefficients representing at least part of an image (IM) in order to insert a set of watermarking signals with a predetermined cardinal, characterised in that it includes the steps of: generating (E 2 ) a set of acceptable segmentations, calculating (E 3 ), for each acceptable segmentation, a probability of error on the detection of the watermarking signals inserted in said each acceptable segmentation, and selecting (E 3 ) a segmentation in the set of acceptable segmentations, by minimising, on all the acceptable segmentations, the probability of error subject to a constraint on the cardinal of the regions of the selected segmentation, with respect to the cardinal (C) of said set of watermarking signals.