When pasting code into Dreamweaver I get a submit query link instead of button gif? Code looks like it is not altered by DW when pasted. It shows button when I add https: to front of //content.authorize.net/images/buy-now-gray.gif
Button shows just fine for me via http. And if you're worried about it not loading properly, you can just download a copy of the image, save it locally, and reference that instead. I always do that anyway because it guarantees fastest load times.