Image: jpg, gif, png, svg

JPG, GIF, or PNG

Description	The alt="" attribute must describe the content of the image
Role	Identifies itself as an image or graphic
Relationships	n/a
State	n/a
Focus	n/a
Action	n/a

Description	The alt="" attribute must describe the content of the image
Role	Identifies itself as an image or graphic - (Use role="image")
Relationships	n/a
State	n/a
Focus	n/a
Action	n/a

Description	The title element of the SVG must describe the content of the image
Role	Identifies itself as an image or graphic - (Use role="image")
Relationships	n/a
State	n/a
Focus	n/a
Action	n/a

The best explanation we've heard comes from an accessibility tester who isn't sighted.

He said, "Good alt text would allow me to describe what's on the page to someone else."