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>
    <allfileusages>
      <f fromid="57" ns="6" title="File:G28PNG.png" />
      <f fromid="19215" ns="6" title="File:Http://i.istockimg.com/file thumbview approve/34031066/1/stock-photo-34031066-beautiful-teenager.jpg" />
      <f fromid="16254" ns="6" title="File:Http://img.photobucket.com/albums/v675/Clavate/My Art/ignudofinishedpainting.jpg" />
      <f fromid="19917" ns="6" title="File:Http://media1.picsearch.com/is?TqfpiKKv1XvKk2e4XqJ4 x52uW94C6RD5ISu-i6jFfI&amp;height=128" />
      <f fromid="22499" ns="6" title="File:Http://media5.picsearch.com/is?4E8Rdy8TXD3-7akubxFvynWl1qirEigCl jL4F7LHa8&amp;height=240" />
      <f fromid="23166" ns="6" title="File:Http://www.socwall.com/images/wallpapers/17993-290x260.jpg" />
      <f fromid="57" ns="6" title="File:Misalligned BeltPNG.png" />
      <f fromid="57" ns="6" title="File:PartinvisePNG.png" />
      <f fromid="57" ns="6" title="File:Settings.png" />
      <f fromid="57" ns="6" title="File:Tg-spndl-spds.gif" />
    </allfileusages>
  </query>
</api>