Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/6727b0ca5edaf124fbe6e3b4e0de93f2.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563