I don't think the API gives access to the full HTML of the page, just the user description so Cachly can't help. You reminded me I too struggle with this when solving puzzles. I hacked together a quick bookmarklet that should help. From Cachly description, use the View in Geocaching.com to open in Safari. Then tap this bookmarklet you will create and it will open the background image in a new tab.
There are numerous "How to create Safari Bookmarklet pages on the web but here is one. http://www.ipadforums.net/threads/guide-creating-safari-bookmarklets.72353/
Here is the bookmarklet definition
javascript:void(window.open(document.body.background))
