FOP fo:display-graphic problem

I'm trying to use fo:display-graphic with FOP, but the graphics appear to be
corrupted in the generated PDF file.

Does fo:display-graphic work in FOP, or am I probably doing something wrong?
I've tried it with GIF and JPEG files from a couple of different sources.
Should I be using a different format?

The XSL-FO follows.
Peter
(Opinions are mine, not my employer's)

--

<fo:root xmlns:fo="http://www.w3.org/XSL/Format/1.0">

	<fo:layout-master-set><fo:simple-page-master
page-master-name="master"><fo:region-body/></fo:simple-page-master></fo:layo
ut-master-set>

	<fo:page-sequence>
		<fo:sequence-specification><fo:sequence-specifier-repeating
page-master-first="master"
page-master-repeating="master"/></fo:sequence-specification>
		<fo:flow>
				<fo:block>
	
http://hilton.org.uk/picture/illustration/hh2.gif
					<fo:display-graphic
href="http://hilton.org.uk/picture/illustration/hh2.gif"/>
					
	
http://hilton.org.uk/picture/photo/belgium/antwerp_hilton_ls.jpeg
					<fo:display-graphic
href="http://hilton.org.uk/picture/photo/belgium/antwerp_hilton_ls.jpeg"/>
					<fo:display-graphic
href="http://xml.apache.org/graphics/index-header.jpg"/>
				</fo:block>
		</fo:flow>
	</fo:page-sequence>

</fo:root>


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