Adding labels to images within rich text

Hi,

I'm wondering if it's possible to add labels to images within a rich text field. I'm able to apply a label to an image, but when I save and publish the document, the label disappears. Am I missing something on how to do this? What I'm trying to achieve is the ability to add classes to images within rich text so that they can align left or right, 50% width or full - is there a different way to achieve this?

Thanks!