Digital images can be analyzed at wide range of levels going from pixel arrangement to semantics. As a consequence, finding a visual complexity estimator is a difficult task. In this article we propose a definition of attention based perceptual complexity. We study the performance of human eye movements and of different models of computational attention against a ground-truth of image complexity based on the observation time of an image description task. The results obtained show that besides its lack of semantic processing, attentional behavior is a good estimator of image complexity.