One problem with using divs with background images instead of proper imgs is divs don't have an exact equivalent of the "alt" tag, for screen readers and webcrawlers.
I found a coworker using "text-align:-9999px;" for the div -- this moved the text off the page but allowed him to use an image instead. (He was concerned about some of the nuance of the font and character rendering.)
It's a clever idea, but I think not a good practice. It smelled a bit off to me, and as I research it I see some bots like Google consider it a bit of a red flag.
A good trick to know of, but I'm not recommending it.