Use this CSS code to use gradient and a background image on the same element.
CSS code:
#id, .class{
background: url([IMAGE URL]), -webkit-gradient(linear, left bottom, left top, color-stop(0, [COLOR]), color-stop(1, [COLOR]));
background: url([IMAGE URL]) 0px -80px, -moz-linear-gradient(center bottom, [COLOR] 0%, [COLOR] 100%);
}
background: url([IMAGE URL]), -webkit-gradient(linear, left bottom, left top, color-stop(0, [COLOR]), color-stop(1, [COLOR]));
background: url([IMAGE URL]) 0px -80px, -moz-linear-gradient(center bottom, [COLOR] 0%, [COLOR] 100%);
}