Google maps V3 infowindow doesn't size to image
===

I'm having some trouble getting my infowindow to have the size that I want. I'm trying to place a 15px x 15px image inside of the infowindow and have the infowindow size itself accordingly. However, it seems no matter what I do the infowindow is much much bigger than the image. Here's the code I am trying to put inside the infowindow:

    <div style="width: 15px; height 15px">
      <img src="http://maps.gstatic.com/mapfiles/transit/iw/6/walk.png" width="15" height="15">
    </div>

Then here's the code to make and display the window itself:

    var infowindow = new google.maps.InfoWindow({
      content: window_text,
      position: GPS_coordinates,
      maxWidth: "15px"
    });
    infowindow.open(map);

Is there something I'm doing wrong here? Thanks for all the help!