Hey there someone02,
There is an option to force login in order to make an appointment, the option is located in Appointments >> Settings >> General, see screenshot http://screencast.com/t/wf8xjDDxByj.
For adding captcha you would need to customize the plugin. However i’m not entirely sure it’s required due to how appsointment+ works, as you have to select days, then times and so on. I’ve never known spambots to utilize this or ever heard reports of it happening from spambots. Appointments+ uses several javascript clicks which spambots aren’t able to reproduce.
Of course I have seen spam, but they were pretty much human spam, and captcha won’t prevent a human from spamming it.
Hope this helps 🙂
Best regards,
Bojan