Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/15eadb61a4b8ac7d89f08ece3999d9d2.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563