Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/6fd51fd3b75c7b9e1f0f97868cd8b634.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563