Add below lines of CSS and done!!!
<style type=”text/css”>
BODY
{
background-image:url(“bg.png”) !important;
background-repeat:no-repeat;
BACKGROUND-COLOR: transparent !important;
}
.s4-ca {
BACKGROUND-COLOR: transparent !important;
}
.ms-alternating,.ms-gb,.ms-alternatingstrong {
background-color: transparent !important;
}
.ms-WPHeader {
background-color: transparent !important;
}
</style>
