The invention relates to a method for estimating a defect in an image-capturing system (I), which produces, with regard to any first image (I), representing any scene (S), a variation in the field of a characteristic of the first image, having an order of magnitude that is statistically lower than a variation in the field of said characteristic added by the scene. The method comprises: calculating, in at least a first portion of the field of the first image, a measurement (μ(I)) related to said characteristic of the first image, an estimative magnitude (ν) of said defect, depending on the calculated measurement and having a variation having the same order of magnitude as the variation in the field of said characteristic of the first image produced by said defect.