This paper analyses the extent to which textbook images are designed using the Instructional Criteria for Image Analysis (ICIA) model in textbooks. The ICIA proposed that learning through images involves interaction between the learner, the image, and the activities with images proposed to the student. Images from the main text and activity section of eleven primary and secondary school textbooks on the human body were analysed regarding the extent to which they fit the proposed criteria. Images in the main text were analysed according to size and type, presence of visual elements (graphical elements, colour, enlarged details), verbal elements (caption, labels) and reference to the image within the text, while images in the activity sections were analysed according to learning involved (task type, procedure, processing level). Results show unequal presence of these criteria in both primary and secondary school textbooks. There are some differences between primary and secondary levels (predominant image type, degree of image contextualisation and processing level required). Images should not be considered self-evident. Images should be designed based less on aesthetic and decorative criteria and more on instructional criteria such as ICIA proposed in order to support image-based learning processes and increase the potential value of images as learning tools.