Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/908a5621ef6a1ff1a6be20cb4a538c9c.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563