The excellent photograph below has fairly standard ALT TEXT: not a lot of detail, but it does give an indication of the graphic file's content.
The pie chart below also has ALT TEXT, but is it descriptive enough? The title "Daily Toast Consumption", which you might expect a screen reader to pick up, is actually part of the graphic. Text on a graphic is invisible to screen readers.
The caption for this graphic says "pie chart". Clearly, that is insufficient to describe the graph to those who cannot see it. So, what would be better?