Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/4f9b03b8a3786f8db20da68e61142eef.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563