Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/c0fdacff10ce3e2e63a5b0a624f6ed4b.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563