1. Method for generating images from source ultrasonic signals obtained by echography, wherein the echos signal is sampled and digitalized to form a succession of samples x.sub.i,j.sup.t as a echographical signal with a coded digital value of luminance X at an instant t, identified in the image by the row i of the horizontal column and the row j of the vertical column to which they belong, wherein said echographical signal is automatically processed to superimpose, on the image, a contour of the analyzed organ by the following steps: reducing the speckle present in said echographical signal through filtration by generating a prediction divergence signal which yields useful data by taking the difference between the digitalized signal x.sub.i,j.sup.t and a prediction signal calculated from a model of speckle, this step of reducing further providing a filtered digital signal F.sub.i,j.sup.t and a binary signal B.sub.i,j.sup.t deduced from the filtered signal produced by said filtration, at state 0 for the points of the filtered signal that have zero luminance and at state 1 for the other points; processing said binary signal to extract from it the data corresponding to echos recognized as being non-characteristic of the contour, and outputting a signal I.sub.i,j.sup.t ; processing said signal I.sub.i,j.sup.t by bridging to minimize discontinuities by eliminating isolated pixels, and outputting a bridged signal I.sub.i,j.sup.t ; processing said bridged signal I.sub.i,j.sup.t to extract from it the characteristics parameters that can be used in a model of the contour of the organ examined, on the basis of a zone of maximum area, called a zero density zone, which comprises only zeros and corresponds to the interior of the organ analyzed; calculating the pixels of the contour on the basis of said extracted characteristic parameters and the equation of the model of the organ; replacing the digital signal, before filtration or when it is filtered, by an overlay signal for all the pixels of the contour; displaying the result of said step of replacing the digital signal by said overlay signal.