Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/c2b0186df83d9e6a9ee0955f5ac1e3a0.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563