This book is an attempt (a successful attempt) in theorising the 'reading' of images. Kress and van Leeuwen, drawing upon Semiotic analysis and Literary Theory, provide a set of tools of analysis to explore the 'visual design' of everyday life (images, films, ads...etc). They refer to this framework as Visual Social Semiotics. i.e., how these visual designs and structure create and generate meaning, and, more specifically, how images communicate meaning and how meaning gets into images. From a background in linguistics, they call for a 'grammar' of the visual. A grammar that will help us 'read' those visual structures in a more functional and structured fashion. The framework Kress and van Leeuwen trace down is characterised by three meta-functions that are believed to be generated in any single visual design, be it an image, a movie, an ad...etc. That is each visual structure performs one of these semiotic functions/task (drawing on the work made by Halliday in linguistics):
1-the representational meta-function
2-the interpersonal meta-function
3-the compositional meta-function
So, each visual structure is thought to be analysed on the light of these semiotic tasks or meta-function.
Kress and van Leeuwen propose a theory they refer to as Modality Markers Theory. They argue that the same way language users elaborate on "modal verbs" to determine the 'certainty' of their statements, images, for instance, also communicate this 'certainty' and 'realness' through the use of 'visual cues' or 'modality markers' (these are being for example the framing, the shot, the position of objects, the composition...etc.). These markers help turning, say, the photograph look 'what counts as real'. Images with 'high modality' seem to be more 'real' and 'reliable' than those with a lower modality.
The book is, to my mind, a further elaboration on the basics (the basics of the Semiotic analysis of media texts) Roland Barthes discussed in his essays "The Rhetoric of the Image", "The Photographic Message" (in Image-Text-Music (1977), the collection of his essays), and further in his book Mythologies (1957) and Camera Lucida (1980).