Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/2bb5c35cb0135e90c40f2fb8b8e23f6c.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563