This is just a simple attempt to prevent automated tools from blasting numerous e-mails to the club, flooding our mailboxes.
So, when filling out the form, just type the characters from the image, into the box provided. What you enter is checked against what is displayed in the image, and if they match, the form will be processed. If the information is wrong, you must go back and re-fill out the form (sorry) and enter the "new" security code that is shown.
Now that you know about the security code field on the forms, you can just close this window to return to the form you were filling out.