Recommending points of interests (POIs) is drawing more attention to meet the growing demand for tours. A POI's quality (sightseeing value) estimation is one of the important challenges. In contrast to conventional studies of ranking POIs based on user behavior analysis, in this paper, we propose methods of quality estimation by analyzing geosocial images. Our approach estimates the sightseeing value from two aspects: (1) nature value; and (2) culture value. For the nature value, we extract image features that are related to favorable human perception to verify whether a POI would meet tourists' psychological requirements. Three criteria, coherence, imageability and visual-scale, are defined accordingly. For the culture value, we recognize the cultural elements (i.e., architectures) included in a POI. In the experiments, by applying our methods on the real discovered POIs, we present the effect of our approach.