Grazie della risposta

mi hai dato un indizio, perché a me il tuo codice genera una serie di errori:

Warning: Cannot modify header information - headers already sent by (output started at C:\Program Files (x86)\Apache Software Foundation\Apache2.2\htdocs\creazione-web\siti-esempio\casaolmata\prenotazioni_xx.php:1) in C:\Program Files (x86)\Apache Software Foundation\Apache2.2\htdocs\siti-esempio\prenotazioni_xx.php on line 517

Warning: imagecreatefromjpeg(img.jpg) [function.imagecreatefromjpeg]: failed to open stream: No such file or directory in C:\Program Files (x86)\Apache Software Foundation\Apache2.2\htdocs\siti-esempio\prenotazioni_xx.php on line 521

Warning: imagecolorallocate(): supplied argument is not a valid Image resource in C:\Program Files (x86)\Apache Software Foundation\Apache2.2\htdocs\siti-esempio\prenotazioni_xx.php on line 522

Warning: imagestring(): supplied argument is not a valid Image resource in C:\Program Files (x86)\Apache Software Foundation\Apache2.2\htdocs\siti-esempio\prenotazioni_xx.php on line 523

Warning: imagejpeg(): supplied argument is not a valid Image resource in C:\Program Files (x86)\Apache Software Foundation\Apache2.2\htdocs\siti-esempio\prenotazioni_xx.php on line 524Insert the control code written in this image: