Brandon, this notice appear because of your PHP version ( most likely your PHP version is lower then 5.3).
1. Find out your version of PHP using steps 1,2,3 under "GD Library" section of this manual:
http://docs.oxwall.org/faq:captcha-troubleshooting
2. If your version of PHP is lower then 5.3, check whether your hosting company can update it for you.
If your host can not update PHP version to 5.3, open error_manager.php
mentioned in your error notice and comment out following line:
//case E_DEPRECATED: