is there a cpecific type of graphic that can do this.This behaviour has nothing to do with graphic format. It's a matter of positioning the image using CSS.
You have two approaches: using a background image, or positioning an img element. Which one you choose will depend on what effect you're after.
body {
background: white url(...) no-repeat fixed 97% 97%;
}This would place an image near the bottom right corner of the browser viewport, and it would remain in the same position even if the viewport is scrolled. Other content in the document would always appear on top of the image.
#logo {
position: fixed;
bottom: -3%;
right: -3%;
}This assumes that you have an img element with the id attribute value, logo. It will position this image close to the bottom right corner of the viewport, and it too will remain in position. Most content in the document will appear below this image.
Unfortunately, IE doesn't support the fixed value for this particular solution (though most other user agents do), and will treat it like absolute instead. You'll have to use a script to keep it in place as the viewport scrolls, though I think the result always ends up looking tacky.
Mike