Ok, let's try it as an upload since that URL is a search result.
Right click on this image, then choose "save as". you should be given the opportunity to choose where on your hard drive to put the image. If not, it typically defaults to your Downloads folder.
Now on Gravatar, go to the same place you were putting the URL. But there's an option to 'upload a photo' instead. Click that. Then use their uploader to put this image there. You'll have to tell it where the image resides on your hard drive.
Once you're all situated there, come back here and try to use the Gravatar again. Make sure you hit the 'test' button beside your email address in our Gravatar window.
Let's see where that gets us.