how to throw error if imagedata not found

[chris snow <chsnow123@gmail.com>]

Is it possible for an error to be thrown during processing if a file
referred to by imagedata is not found?

    <mediaobject>
      <imageobject>
        <imagedata fileref="../../images/coding-cycle.png"/>
      </imageobject>
    </mediaobject>

Many thanks,

Chris