Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/5fb8c2f7a405718f7f0ae33a48f2a1f7.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563