Sentence:  Drawings and <WSD>pictures</WSD> are more than mere ornaments in scientific discourse. Blackboard sketches, geological maps, diagrams of molecular structure, astronomical photographs, MRI images, 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:  A representation of anything (as a person, a landscape, a building) upon canvas, paper, or other surface, by drawing, painting, printing, photography, etc.