Any idea how to implement a pop-up window just big enough for an image? I don't know what size images are going to be uploaded.

This is how I've done the pop-up, and it works:

pages.xml

<page view-id="/search.xhtml">
 <navigation from-action="#{searchSessionBean.setPhoto}">
 <render view-id="/hppu.xhtml"/>
 </navigation>
</page>

and on the view:

<h:column>
 <f:facet name="header">Show the Photo</f:facet>
 <s:link target="PopUp" onclick="window.open(null,'PopUp','width=270,height=290')"
value="Show the Photo" action="#{searchSessionBean.setPhoto}" />
</h:column>

Incidentally, not using pages.xml and supplying the URL of the pop-up page does not work. The page that pops up is the same as the page on which the link was clicked. The same goes for using navigation.xml