Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/2a7e872754155f80dc7ebb6c79814e76.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563