When you hire an IC to create a work of authorship such as a computer program, written work, artwork, musical work, photographs, or multimedia work, you need to be concerned about copyright ownership.
The copyright laws contain a major trap for unwary hiring companies. The hiring company will not own the copyright to the IC's work unless it obtains a written assignment of copyright ownership. An assignment is simply a transfer of copyright ownership. You should obtain an assignment before the IC starts work. This assignment should be included in the IC agreement.
There are exceptions to this rule. Certain specially commissioned works by ICs are considered to be works for hire, to which the hiring company owns the copyright. However, this rule is not automatic -- you still have to enter into a written agreement explicitly stating that the work is for hire.
For more information, see How to Protect Your Intellectual Property Rights in Works Created By Contractors.
For a complete guide to the ins and outs of working with independent contractors, get Working With Independent Contractors, by Stephen Fishman (Nolo).