While updating some Latex for the JHU ACM, I wondered if it would be possible to put an image file with our logo on it in the title page. Turns out, someone wondered the same thing and eventually created the titlepic package in 2008. Its use is really easy:
\titlepic{\includegraphics[width=\textwidth]{cover.jpg}}It's got a couple options for customization, and there's a solution in the comments on http://typethinker.blogspot.com/2008/08/picture-on-title-page-in-latex.html for putting your picture above the title, as I did.
\maketitle