unable to include image using <imagedata> into PDF file

I am unable to get an image into a PDF file. Here's the XML source:

<mediaobject>
<imageobject>
<imagedata fileref="img/david-bowie-001.jpeg"/>
</imageobject>
</mediaobject>

I use the FOP processor to render the PDF and get this error:

     [java] Jun 19, 2009 6:40:46 PM org.apache.fop.fo.flow.ExternalGraphic bind
     [java] SEVERE: Image not available: url(img/david-bowie-001.jpeg)