Sentence:  Drawings and pictures are more than mere ornaments in scientific discourse. Blackboard sketches, geological maps, diagrams of molecular structure, astronomical photographs, MRI <WSD>images</WSD>, the many varieties of statistical charts and graphs: These pictorial devices are indispensable tools for presenting evidence, for explaining a theory, for telling a story. 
Meaning of the word marked with <WSD> tags:  An optical or other representation of a real object; a graphic; a picture.