Hi Liz –
First – I am not an attorney- I would highly recommend you seek out the advice of one who specializes in intellectual property law for a real opinion.
That said, there is much written about whether what we do is (or should be) considered a work for hire. It has been my understanding that unless specified otherwise in a written contract it is, which limits your rights and strengthens theirs.
If you wanna make your head spin, do a google search and read: click here
