I'm not sure of exact rules, but from my reading and what I've been doing, I have tables (showing data, etc), figures (graphs, charts, etc), and images (pictures, drawings, etc).
I don't think there are official rules on what you call them, but if they're taken off someone else, just make sure you reference them in the normal harvard way: (Someone et al, 1999) under the image, then properly reference in references section.
hope that makes sense.