Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/50b0a5e21f1d6df773d4757938747e66.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563