I'm computing the cost basis of a home I sold. I put a new deck on the house a few years back. I have photos but no receipt. How can I calculate the cost?

You would need to look at old bank statements or credit card statements from the time to figure out what you paid for the materials or what you paid the contractor.  If you hired a contractor, it is possible that they still have the records and you could contact them to find out what you paid.