1. A method for associating the content of a digital image with a class of a classification system, wherein the image is represented by N pixels, each pixel being located at the position (x i , y j ) in a predetermined coordinate system, said image extending from the coordinates (0, 0) to (x imax , y jmax ) and imax being the maximum number of pixels in the direction of the x-coordinate and jmax is the maximum number of pixels in the direction of the y-coordinate and wherein at least one numerical content attribute data [j, i] is associated with each pixel, said method comprising the steps of: determining at least one group of a predetermined number of F numerical shape attributes ψ m with m as a running index, wherein ψ m is a transformed expression of the moment ρ m , and ρ m is derived from ρ m _ = k m ⁢ R m _ with ⁢ ⁢ k m = ( m + 2 ) 2 ⁢ ( π  A  ) m 2 A = m 0 , 0 = Δ ⁢ ⁢ a ⋆ Δ ⁢ ⁢ b ⋆ ∑ j = 1 j ⁢ ⁢ max ⁢ ∑ i = 1 i ⁢ ⁢ max ⁢ data ⁡ [ j , i ] R m _ = υ m υ 0 = υ m m 0 , 0 υ m = Δ ⁢ ⁢ a ⋆ Δ ⁢ ⁢ b ⋆ ∑ j = 1 j ⁢ ⁢ max ⁢ ∑ i = 1 i ⁢ ⁢ max ⁢ ( R ⁡ ( j , i ) ) m ⁢ data ⁡ [ j , i ] R ⁡ ( j , i ) = ( ( i - 0 , 5 ) ⋆ Δ ⁢ ⁢ a - x _ ) 2 + ( ( j - 0 , 5 ) ⋆ Δ ⁢ ⁢ b - y _ ) 2 x _ = m 1 , 0 m 0 , 0 y _ = m 0 , 1 m 0 , 0 m 1 , 0 = ( Δ ⁢ ⁢ a ) 2 ⋆ Δ ⁢ ⁢ b ⋆ ∑ j = 1 j ⁢ ⁢ max ⁢ ∑ i = 1 i ⁢ ⁢ max ⁢ ( i - 0 , 5 ) ⋆ data [ j , i ] m 0 , 1 = ( Δ ⁢ ⁢ b ) 2 ⋆ Δ ⁢ ⁢ a ⋆ ∑ j = 1 j ⁢ ⁢ max ⁢ ∑ i = 1 i ⁢ ⁢ max ⁢ ( j - 0 , 5 ) ⋆ data [ j , i ] wherein Δa=width of the pixel in the x-coordinate direction, Δb=width of the pixel in the y-coordinate direction, data [j, i]=content attribute of the pixel at the position (y j , x i ) m=a number running from 1 to F as a counter of the shape attributes; comparing the value of each shape attribute of the F numeric shape attributes intended for the picture in the at least one group with the value saved in a table for the respective shape attribute of this group, wherein values for the individual numerical shape attributes of this group in the table are associated with each class; and outputting the class as an association class in which the image to be recognized is classified, in which the F numeric shape attributes intended for the picture best correspond to the values of the numeric shape attributes recorded in the table for this class.