How do we go about verifying I-9 documents for remote employees?

Q. We have a workforce that largely works remotely, some hundreds of miles from our corporate office. For a variety of reasons, we will be reclassifying a number of these individuals from independent contractor status to employees. Given that we will need I-9s for the employees, do we need to personally see the required identification documents, or can the employees send us facsimiles/scans, etc.? If we need to see the forms personally, what is the best way to do that?