how to add image validation in zfdatagrid

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What steps will reproduce the problem?
1.my code
 $zendForm->addElement('file', 'FileName', array('label' => 'Upload Logo'));
        $zendForm->getElement('FileName')
                 ->setDestination('images/openlogo/')
                 ->setRequired(true);

2. I want to add validation so that user can only upload jpg,png images

What is the expected output? What do you see instead?

I want to shw error message if user upload any other document

Please insert the appropriate values;
Zend Framework version:
ZFDatgrid Version (Bvb_Grid::getVersion()):
Operating system:
PHP Version:
Database Server and version:
Source Adatapter:

Please provide any additional information below.

Original issue reported on code.google.com by prachiwaliaodesk on 24 Dec 2013 at 10:16