We evaluate a preprocessing method for image compression artifact reduction based on nonlinear diffusion filtering that we proposed earlier. The method consists of using edge-adaptive diffusion processes before the discrete cosine transform (DCT)-JPEG compression. By using a simple measure for artifact reduction, we show that considerable artifact reduction is achieved with preprocessing at the same bit rate as, and with no greater error than, the original compression. We also show that preprocessing helps to preserve the true contours for image processing applications. An automatic parameter selection for the preprocessing is also proposed, considering the edge histogram of the image and depending on the compression ratio. We test the method for visual quality with extensive subjective measurements. We show that, depending on the image content, preprocessing can significantly improve the visual quality at low bit rates.