You can add new image to '/templates/ot_rendcore/images' folder.
And then edit file '/templates/ot_rendcore/css/preset-style-1.css', '/templates/ot_rendcore/css/preset-style-2.css' and '/templates/ot_rendcore/css/preset-style-3.css'
Line 413
.oBottomBlock2{
background-color: #FFFFFF;
-webkit-box-shadow: 0 1px 3px rgba(0, 0, 0, 0.15);
-moz-box-shadow: 0 1px 3px rgba(0, 0, 0, 0.15);
box-shadow: 0 1px 3px rgba(0, 0, 0, 0.15);
}
change to
.oBottomBlock2{
background-attachment: scroll;
background-image: url("../images/{image}");
background-repeat: no-repeat;
background-position: 0 0;
background-color: #FFFFFF;
-webkit-box-shadow: 0 1px 3px rgba(0, 0, 0, 0.15);
-moz-box-shadow: 0 1px 3px rgba(0, 0, 0, 0.15);
box-shadow: 0 1px 3px rgba(0, 0, 0, 0.15);
}
background-repeat: no-repeat / repeat