Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/3a31ca8e87a57ae27b4ef6a69fe96a16.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563