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>
    <allfileusages gafcontinue="Lamp_tavern_ls.jpg" />
  </query-continue>
  <query>
    <pages>
      <page ns="6" title="File:Imagename.jpg" missing="" />
      <page pageid="50" ns="6" title="File:Birmingham-conservatoire01.jpg" />
      <page pageid="39" ns="6" title="File:Cafe ort img 5455-2.jpg" />
      <page pageid="77" ns="6" title="File:Club db.jpg" />
      <page pageid="52" ns="6" title="File:Eagle inn salford.jpg" />
      <page pageid="70" ns="6" title="File:EarCleaning.jpg" />
      <page pageid="148" ns="6" title="File:Eggtimer ballo tacettop crop2.png" />
      <page pageid="28" ns="6" title="File:Greenhouse p1010117.jpg" />
      <page pageid="30" ns="6" title="File:Gregson-lg.jpg" />
      <page pageid="42" ns="6" title="File:Harehounds Venue-1.jpg" />
    </pages>
  </query>
</api>