You could do something like this:
@media only screen and (max-width:767px){
.header{
text-align: center;
}
.header{background:none}
.header:after{
content:"";
display:inline-block;
width:100px;
height:50px;
background: url(http://placehold.it/100x50) no-repeat 0 0;
vertical-align:middle;
}
}