show a phone number a picture was taken on

The company I work for, we hire realtors to go and inspect properties, including taking pictures of. We, the company, needs to make sure that the realtor is taking the picture, and is not sending some else to do it. So far, the only way that comes to mind is seeing the phone the pictures were taking with, and double check that number with the realtor’s phone number on record.

I will appreciate all your help.