In general its bad practice to put images in the H1. This doesn't mean if you just stuff a few keywords in them that you'll rank better either. But the Header tags are meant to hold text - text that accurately describes to the reader what they should expect to see below the header.
Bill's article on headers is fantastic.
And the original source from w3.org says:
"A heading element briefly describes the topic of the section it introduces...." - basically that it's meant for text. Source
So as Bill says, if you correctly set up a semantic relationship between the title, headers and content on the page, you can help users and engines understand what the page is "about" and thus rank better in that sense.
Hope that helps!!
-Dan