Layout

I'm using the Magazine template for a photoblog. For posts with multiple images, I create a Markdown file with image embeds and a float right {>>} tag on square or landscape images so they are displayed in a similar size as portrait images. However, when posting single images directly, I'm unable to add those tags since there's no Markdown. Is it possible to add the applicable .css class to square and landscape ratio image posts through the template directly? Two examples links from my site: multi image post vs single image post