In some contexts, a photograph may be worth a thousand words. Previous research revealed a dialectical character of photographs: they simultaneously lack determinacy and exhibit an excess of meaning. The purpose of this study was to understand how, under this condition, high school students interpret photographs that were accompanied by different amounts and types of cotext (caption, main text). The data for this study consists of video-recorded interviews with twelve Brazilian high school students. What students perceived was in part a function of the presence of caption and main text; these texts not only described what could be seen but also taught students how to look at photographs. We conclude that high school students not only need to develop subject matter literacy but also a literacy concerning photographs to fully understand their textbooks.