Any information that is valuable to the user should not be strictly an image. If the user might find the information useful, it should be able to be customized to fit their needs.
Images of text should be avoided. Certain assistive technologies include character limits for alt text and overly verbose alt descriptions lead to a poor user experience.
Graphs, screenshots, and diagrams that convey information that is more than just text must include a written description of the data or include data in charts as HTML tables.