Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/688d8a27f2bb435b312341d17252a2e0.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563