After having read and worked with Machin & Mayer’s (2012) book How to Do Critical Discourse Analysis, I have started to read Reading images: the grammar of visual design by Gunther Kress and Teo van Leeuwen, where the authors examine the ways in which images communicate meaning. This book is not available as a free preview to embed, but I link to an extract HERE and at Google books there is an extract from the 1st edition from 1996 available.
Kress, G. & Van Leeuwen, T. (1996). Reading images: the grammar of visual design. London: Routledge.
Kress, G.R. & Van Leeuwen, T. (2006). Reading images: the grammar of visual design. (2. ed.) London: Routledge.