Visual literacy is the ability "to understand and analyze the contextual, cultural, ethical, aesthetic, intellectual, and technical components involved in the production and use of visual materials." (source)
To understand what you're seeing, ask yourself the following questions.
Tools to help you discover the original source of an image.
Data visualizations like charts and graphs can present information in a more direct and engaging way than text alone. Like text, they can also present information in biased and misleading ways, so it's important to understand what you see.
The two images below represent the same set of data reported by Patient.info. Which one does a better job? Why?