@ahojnnes @JDWarner @stefanv I guess this does not quite make sense.
It should go like the 'correlation coefficient *between* the image and the template'.
Maybe something explanatory could elaborate along the lines
"The output is an array with values between -1.0 and 1.0. The value at a given position corresponds to the correlation coefficient between the image and the template (picture the template scanning the image over all possible positions [note to self: check whether centre or upper left corner is used as position] to find the best match: the best match is given by the largest value of the correlation coefficient)."