When it comes to protecting your work, the reality is that you can do things to discourage copying but you can’t stop it from happening.
To try to slow clients from making copies, you can use textured prints and stamp the back of all your prints with your copyright info. Many customers don’t even realize they are stealing, but some do and the technology is readily available to do so easily. Many photo places are getting better at stopping the reprinting of copyright info but it will never be 100%.
A good solution is to structure your pricing and make money from the sitting fees and charge a reasonable amount on the prints. If your print prices are reasonable the customer is likely to buy the prints from you instead of going to the photo lab and getting questionable results. Many photography businesses do this the other way to keep the perceived cost for the customer low by charging little to nothing for the sitting fee and charge a significant amount for the prints. If your shoot cost is low and photo prices high, you will get a minimum purchase from many customers and they will then go and scan the photo and make their own copies.