Detect if google.maps.MarkerImage object is empty
===

I have a Google map that is being populated by several markers. I am getting my markers from http://chart.apis.google.com/chart?chst=d_map_xpin_icon&chld=pin|glyphish_star|FFFF00|0000FF.  Some of my clients browser security prevents these images from being downloaded and i would like to detect this and revert them to a default image.

    var gmMarkerImage = new google.maps.MarkerImage(
      "http://chart.apis.google.com/chart?chst=
        d_map_xpin_icon&chld=pin|
        glyphish_star|
        FFFF00|
        0000FF"
    )

How do i detect if gmMarkerImage object is not a image or empty? Or how do i determine that I did not receive anything from the chart.apis.google.com site?
