Eek, in my experience text H2 has definite value. If your dead on doing this, make sure you give the image a decent alt tag.
We're at a point, right now, pre-HTML5, where if using text for things like headings isn't viable in the design, I'd redesign. If you don't have great headings, and your competior does, you've got to do way more offsite stuff to keep up. Your potentially creating a mammoth task down the line in the name of saving a bit of time now. Shortcuts make long journeys and all that.