CAPTCHA needs the GD and FreeType libraries installed and enabled on your PHP server in order to work. You can check this by going to Administration -> Site -> System Information -> PHP Information.
Please contact your server administrator if they are unavailable.
Other common problems are:
- If you've created your own translation, please make sure you have used the HTML character code equivalents for UTF-8 characters. If you've chosen not to, make sure that the file is saved as UTF-8 without BOM. The BOM (byte order mark) displays garbage characters when loaded and this could cause the JPEG output of CAPTCHA to be misinterpreted, rendering it unusable.
- If you are using a caching component, make sure that RSForm! Pro is not cached.
- Change the session handler. To do so, head to System >> Global Configuration >> System and set Session Handler to No.
- CAPTCHA within 2 forms on the same page, one CAPTCHA field doesn't work. If you are displaying 2 separate forms, both containing a CAPTCHA field, on the same page, make sure to provide different names for the CAPTCHA fields in order for both of them to work properly.