That is generally true if it was a work for hire. But a work for hire means making them an employee (requiring an employment contract and a host of legal regulations) or a contract to do the work assigning the rights as though it was a work for hire (requiring a contract that assigns rights).

Either way a contract is needed, and the appropriate professional to write either contract is a lawyer.

Back to the original problem: Use the right professional for the job, and if you can't get a lawyer then you probably aren't ready for the real business world.