Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/07b7b7dc9b7a8e7262f19b0c3e2d6a06.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563