how to get image source from an img tag using php function.
Consider taking a look at this.
I'm not sure if this is an accepted method of solving your problem, but check this code snippet out:
// Create DOM from URL or file
$html = file_get_html('http://www.google.com/');
// Find all images
foreach($html->find('img') as $element)
echo $element->src . '
';
// Find all links
foreach($html->find('a') as $element)
echo $element->href . '
';