In atomic force microscopy, tapping-mode (also called intermittent contact mode) operation is known for its ability to image soft materials without inducing severe damage. For soft materials, the determination of the relative contributions of the topography and the local mechanical properties to the recorded image is of primary importance. In this paper, we report a systematic comparison between images and approach-retract curve data. We show that this experimental comparison allows the origin of the contrast that produces the image to be straightforwardly evaluated. The method provides an unambiguous quantitative measurement of the contribution of the local mechanical response to the image. To achieve this goal, experimental results are recorded on a model system, a triblock copolymer, with a nanophase separation between elastomer and glassy domains. In this particular case, we show that most of the contrast in the height and phase images is due to variations of the local mechanical properties.