Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/455d7fcaa16c0a3a543a0ec3c2e2b2af.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563