Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/3f69897b75aad1d8cffb0d67a216c7e1.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563