Copy this code and put it in an "HTML" gadget. If you need detailed instructions go HERE.
<style type="text/css">body{background-image: url('https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiCR7Jx1uWzPzt2Z2ElkfdGgp9ppChr2Z9ydb2ohL16CF5Ot_qKI4FexlmMG9ZIWreyw45Zy8TytKYKk062lRg3hAwZ6Ktmje7SLhIeH5o4bxzW6OFQmq-E_loQzQDt2YgSbCwCo7hzHbQ/s1600/Slide4.JPG');background-position: top; background-repeat: no-repeat; background-attachment: fixed; }</style><div id="tag" style="position:absolute; top:10px; left:0px;border:0px;"><a href=http://www.designsbyfarmgirl.blogspot.com target="_blank"><img border="0" src="http://i1213.photobucket.com/albums/cc463/MNFarmGirl/backgrounds/DBFGLogo.gif" width="185"/></a></div>