Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/5f86ae0be6fb7c989f7b20d0f0c433e6.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563