What we see is not only a function of the visual features entering our eyes, but also our knowledge and expectations of what we think we will see. These expectations govern how well we will see an image. When comparing unusual images and matched controls in a demanding detection task, observers were significantly more accurate at detecting the control pictures compared to the unusual ones, even though no machine vision system could distinguish between them (Greene et al, AP&P 2015).
Top-down knowledge is also reflected in patterns of eye movements. Idiosyncrasies in individual eye movement patterns can be accurately decoded from summary statistics, while an observer's task cannot (Greene, Liu & Wolfe, Vision Research 2012).