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/AVvXsEg0kyJURfYIxoWq3J7LfLmF8YyBdq4G8Vfu3m772Ib0V5JTjZP3R5kRnMnnGmumsQlZuYfUfJSctWdX6Etw5QBiPF1MhSicH07YjIDmKd-qkD2WkiOW8xE8jcbt1w14RCgcoaSruRvXi9s/s1600/Slide7.JPG');
background-position: center; background-repeat: no-repeat; background-attachment: fixed; }</style><div id="tag" style="position:absolute; top:30px; 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>