Subjective image-quality estimation with high-quality images is often a preference-estimation task. Preferences are subjective, and individual differences exist. Individual differences are also seen in the eye movements of people. A task's subjectivity can result from people using different rules as a basis for their estimation. Using two studies, we investigated whether different preference-estimation rules are related to individual differences in viewing behaviour by examining the process of preference estimation of high-quality images. The estimation rules were measured from free subjective reports on important quality-related attributes (Study 1) and from estimations of the attributes’ importance in preference estimation (Study 2). The free reports showed that the observers used both feature-based image-quality attributes (e.g., sharpness, illumination) and abstract attributes, which include an interpretation of the image features (e.g., atmosphere and naturalness). In addition, the observers were classified into three viewing-strategy groups differing in fixation durations in both studies. These groups also used different estimation rules. In both studies, the group with medium-length fixations differed in their estimation rules from the other groups. In Study 1, the observers in this group used more abstract attributes than those in the other groups; in Study 2, they considered atmosphere to be a more important image feature. The study shows that individual differences in a quality-estimation task are related to both estimation rules and viewing strategies, and that the difference is related to the level of abstraction of the estimations.