Just copy this script to: design/custom style sheet/CSS code
change in the parenthesis with your picture url


but earlier, you must upload your picture to file: My page/files/choose/upload files
open uploaded so copy the url to parenthesis:

#top2 { background:#1d7028 url(http://files.myopera.com/masthebee/files/lufi2.jpg); }

lets try it my friend,dont forget to choose "Use my custom style sheet together with the current blog design" and save it, the reaction not immedietly, you must change design,the effect will complete..