The term "Visual Literacy" was first coined in 1969 by John Debes. According to Debes, "Visual Literacy refers to a group of vision-competencies a human being can develop by seeing and at the same time having and integrating other sensory experiences literacy is used to help students to learn how to read." In other words, visual literacy involved the ability to understand visual messages. This includes visual texts, such as a documentary, or visual information, such as a charts, graphs or diagrams.
Visual literacy allows for people to demonstrate meaning in literacy in a creative way.
The images are a way to express ideas or information with or without using words to explain these ideas.
A person who is visually literate, is able to produce meaning from an idea that is represented by some type of image.
Images serve as representations of ideas, however there is also some room for interpretation, by those who are viewing the images.
Visual literacy can be helpful for ESL(English as a second language) students because the images presented, may be universally recognizable. ESL students may be able to identify with the images or make connections with the images to their own culture.
Sources: http://k-8visual.info/http://www.kn.pacbell.com/wired/21stcent/visual.html
http://www.ivla.org/org_what_vis_lit.htm#definition
http://www.learninglive.co.uk/teachers/primary/literacy/materials/visual_literacy/index.asp