<img style="float: left; width: 100px; height: 100px;">
<div>
    <br style="clear: both;">
    <img style="float: left; width: 100px; height: 100px;">
</div>
<img id="target" style="float: left; width: 100px; height: 0; background-color: blue;">
<script>
    document.body.offsetTop;
    document.getElementById("target").style.height = "100px";
</script>