In a background property you can add background-color, repeat, no-repeat and other image attributes, but in the background-image property you are only allowed to add image.
background-image: url("img_tree.png");
background-repeat: no-repeat;
background-position: right top;
background-attachment: fixed;
and in background property you can do in one line all these
background: #ccc url(paper.gif) no-repeat;