Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/5aa5e08e91ca8cb48a2501f44a71f2b0.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563