1. A method for signal evaluation of an electronic image sensor in the course of pattern recognition of the image content of a test body including; dividing the image of said test body into a group of N×N grid-like windows each of the size of n×n pixels; generating a multiple pixel output signal representing image content in an n×n pixel window within an N×N window of the image of said test body; analyzing the image content in one of said n×n pixel windows by converting said output signal into at least one invariant characteristic value using at least one calculation specification in the form of a two-dimensional mathematical spectral transformation method selected from the group comprising a Fourier, Walsh, Hadamard or circular transformation; defining two dimensional spectra from said image content; calculating spectral amplitude values from these two-dimensional spectra and linking together said spectral amplitude values; weighting said characteristic value with at least one indistinct affiliation function, said affiliation function being a functional connection with a value range of said characteristics value and a characteristic; generating a higher order indistinct affiliation function by conjunctive linking of all of said affiliation functions of said characteristic; determining one sympathetic value from said higher order affiliation function for each n×n pixel window, said sympathetic value defining a degree to which a characteristic in said image is similar to a reference characteristic; comparing said sympathetic value with a threshold value; deciding a class affiliation for said signal from said comparison of said sympathetic value and said threshold value; and wherein converting said output signal into at least one invariant characteristic value includes generating an invariant spectrum, and wherein the invariant property is adjustable by using transformation coefficients.