Wanted to share since I just finally figured out how to get the image to work instead of using TheKnot.com's ugly grey button.
It's actually really simple, above the text box where you write all of your descriptive info is an editing button called "source" with an icon of a piece of paper next to it. Click this button, it will change how the info in your text box looks, paste the link that starts with <divstart and ends with </div<, and you should be all set! Then just click below on "preview" to be sure everything looks just how you would like it.