Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/29251d98db1dc3f6b0b5b2b8a5a61fe2.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563