To get Antibot and Human SPAM detection for contact forms, you can use Shield's built-in SPAM detection system to identify contact form SPAM.
The settings can be found under the Integrations module => SPAM Detection:
All you need to do is to enable antibot or human SPAM detection options (or both) and select the contact form provider you want to apply the settings for.
Note: Antibot and Human SPAM detection for contact forms feature is available with Shield Pro only. To find out what the extra features for Shield Pro are, read the article here.