It might be easier to do the podcast-icon thing with sandbox. It generates styles based on post content. So if you put all your podcasts in the ‘podcast’ category, sandbox would automatically assign the ‘category-podcast’ style to the div surrounding the post. You could then apply that CSS to put in the image without ever touching the markup / code.

Of course you would need a theme that supports it, but it’s totally worth looking into. It’s saved me tons of time and effort.