Verbal Versus Visual: A Word Is Worth a Thousand Pictures, Too
http://www.ingentaconnect.com/content/stc/tc/2002/00000049/00000002/art00010
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  peer-reviewed

Doumont, Jean-luc
Technical Communication Online
2002

Abstract:

A picture is worth a thousand words, or so the saying goes—a saying debated by some but accepted pragmatically by most. Do we not all remember some little drawing or other that came in handy to clarify an otherwise plainly unintelligible discourse? Professionally, experienced technical communicators know the benefit of adding illustrations to the text of their technical publications. With increasingly better tools available for their production, pictures seem to have a bright future indeed.