You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query-continue>
    <allimages gaicontinue="100YBP_Delft_Presentation14.jpg" />
  </query-continue>
  <query>
    <pages>
      <page pageid="2620" ns="6" title="File:000.jpg" />
      <page pageid="994" ns="6" title="File:02P2Mary17.jpg" />
      <page pageid="995" ns="6" title="File:02P2Mary18.jpg" />
      <page pageid="996" ns="6" title="File:02P2Mary47.jpg" />
      <page pageid="2622" ns="6" title="File:0506-holl.jpg" />
      <page pageid="1504" ns="6" title="File:1.jpg" />
      <page pageid="344" ns="6" title="File:100YBP Delft Presentation10.jpg" />
      <page pageid="345" ns="6" title="File:100YBP Delft Presentation11.jpg" />
      <page pageid="346" ns="6" title="File:100YBP Delft Presentation12.jpg" />
      <page pageid="347" ns="6" title="File:100YBP Delft Presentation13.jpg" />
    </pages>
  </query>
</api>