Modeling image naturalness has been a very challenging topic. The ideas in this work represent a new approach, since earlier studies considered only memory colors. Perceived naturalness was assessed for eight test images and their 22 manipulations. These were rendered in the lightness, chroma, or sharpness domain using a nine-point qualitative category scale. From the results of psychophysical experiments, four visual phenomena were determined to be important factors in the judgment of naturalness. These factors were modeled using three components–image sharpness, image colorfulness, and reproduction of shadow detail (and the absence of a washed-out appearance)–in an image naturalness model. Correlates of the three components were derived using parameters optimized from color-appearance attributes and pixel-based color difference in CIECAM02 and CAM02-UCS space. It was demonstrated that the developed image naturalness model could predict well the perceived naturalness changes arising from images varying in the lightness, chroma or sharpness domains. Additionally, it was also argued that the application of memory colors to modeling naturalness is not sufficient.