The only other issue is that if you read the terms of use for stock images from Shutterstock as well as other stock sites, is that using their art for logos is strictly forbidden. If you use it anyway, there is embedded information in each piece of art you license that can be tracked with software that monitors illegal use. If they find their art in your logo, they will make you remove it from your site. If you do not, you could end up paying a pretty stiff fine for violating the terms of use. Proceed with caution. Otherwise, find an image that has no strings attached. Try clker.com for public domain images.
To inline an image in a webpage, it must be a browser-supported type - generally PNG, GIF or JPEG. JPEGs are best for photos, PNG for line drawings and things with sharp edges.
Modern browsers do support SVG vector graphics, but not I believe inline only as a separate object, and older browsers and maybe portable devices won't.
Flash is also possible for an embedded object, and you could probably find a code that would display a vector drawing. Personally I find those really annoying - they look great on a modern browser on a new computer on a fast connection, but everywhere else they are broken or slow and a stupid choice for something that appears on every page.
