めちゃくちゃ簡単やな。。
var canvas = document.getElementById('canvas')
var dataurl = canvas.toDataURL();
alert(dataurl);
$element = new Zend_Form_Element_File("test");
$temp = tempnam("/tmp","form_");
$element->addFilter('Rename', array(
'target' => $temp,
'overwrite' => true,
));
$element->receive()
Zend_Debug::dump($element->getFileName());
Zend_Debug::dump($element->getMimeType());