table.dataTable thead .sorting {
    background: url("../images/sort_both.png") no-repeat center right;
}
table.dataTable thead .sorting_asc {
    background: url("../images/sort_asc.png") no-repeat center right;
}
table.dataTable thead .sorting_desc {
    background: url("../images/sort_desc.png") no-repeat center right;
}