width: xxxpx; /* the width of your branding png */
height: xxxpx; /* the height of your branding png */
overflow: hidden; /* so the div contains its contents */
background: transparent url('background.png') left top no-repeat;
This sets the image you want as the branding as a background to the DIV and hides the text by moving it out of the browser window to the left, but Google and friends can still read it.