Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/74a4bdcd1b3586bdea3d7c4f58f33f12.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563