background: #6cab26;
background-image: url(IMAGE_URL); /* fallback */
background-image: url(IMAGE_URL), -webkit-gradient(linear, left top, left bottom, from(#444444), to(#999999)); /* Saf4+, Chrome */
background-image: url(IMAGE_URL), -webkit-linear-gradient(top, #444444, #999999); /* Chrome 10+, Saf5.1+ */
background-image:    url(IMAGE_URL), -moz-linear-gradient(top, #444444, #999999); /* FF3.6+ */
background-image:     url(IMAGE_URL), -ms-linear-gradient(top, #444444, #999999); /* IE10 */
background-image:      url(IMAGE_URL), -o-linear-gradient(top, #444444, #999999); /* Opera 11.10+ */
background-image:         url(IMAGE_URL), linear-gradient(top, #444444, #999999); /* W3C */

http://stackoverflow.com/questions/2504071/is-it-possible-to-combine-a-background-image-and-css3-gradients

Background Image and CSS3 Gradient

css, image, background

CSS