An ID Capture field can be added to your check in flow by editing your button(s). Scroll down to the visitor fields section and to the right, and when adding a field select the ID Capture:
There are two types of IDs that can be captured: Driver's License and Passport. Click on the ID icon to switch between types. If you have Returning Visitors turned on, then you can click on the lock icon to make the field "required" or "always required":
Please note that unlike other visitor fields, the ID Capture field cannot be made "optional" to your visitors; therefore, the field cannot be skipped during the check-in process. To activate this feature, update The Receptionist app to version 4.4.0 or newer.