<div id="tagcontainer"><img id="tagimg" src="img/tri.png"/></div>

#tagcontainer {
    width:100%;
    top:0;
    position:absolute;
}
    #tagimg {
        position:relative;
        margin:auto;
    }

#tagimg {
        display:block;
        position:relative;
        margin:auto;
    }

#tagcontainer {
width:100%;
position:absolute;
}
#tagimg {
width:[imagewidth]px;
top:0;
position:relative;
margin:auto;
}