Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/18b1600d703b1d3b7398c5b99934f8ed.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563