Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/b5d55abc28a8d72fee0dc23ac3a5d3a5.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563