The counter algorithm has been presented to detect pairs of similar numerical strings in order to distinguish between a subset of identical signals and other signals. The pair of similar signals is determined using the matrix of the algorithm. Two elements of the matrix estimate the similarity degree in contrast to the ordinary applied a single value of correlation coefficient. The matching of signal images with the matrix elements has been made on an example of impulse signals. Using this data type we compare the outcomes of two methods: a counter based technique and the correlation method. The difference between the method proposed and the correlation method is discussed.