TCAdmin supports captcha from adscaptcha.com. They have free security only captchas and captchas that allow you to make money with ads.
To enable adscaptcha support create a text file at TCAdmin Control Panel\Web\adscaptcha.config with the following:
<configuration>
<appSettings>
<add key="CaptchaId" value="your-captcha-id" />
<add key="PublicKey" value="your-public-key" />
<add key="PrivateKey" value="your-private-key" />
</appSettings>
</configuration>
