A method for estimating quality of images compressed with a transformation based compression method. The estimation method uses estimated errors generated by quantization to obtain an image quality indicator and does not require use of a reference image. The estimation method includes calculating a probability of at least one specific quantized transformation coefficient value for at least all coefficients representing one identical two-dimensional frequency, and estimating identifying parameters of at least one probability density function of non-quantized coefficient values from the quantized coefficient value probabilities, with a type of probability density function being preset. The estimation method further includes calculating an image quality indicator from errors introduced by quantization, which are derived from probability density function parameters and quantization parameters.