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>
    <pages>
      <page pageid="1" ns="0" title="Main Page">
        <images>
          <im ns="6" title="File:OpenCellID I want to use the data2.png" />
          <im ns="6" title="File:OpenCellID how to contribute2.png" />
          <im ns="6" title="File:OpenCellID how to join2.png" />
          <im ns="6" title="File:OpenCellID scoring lists2.png" />
          <im ns="6" title="File:OpenCellID view the data2.png" />
          <im ns="6" title="File:What is OpenCellID2.png" />
        </images>
      </page>
    </pages>
  </query>
</api>