Do I have to have a business license prior to purchasing equipment for the business?

I am thinking of starting a home-based photography business. Do I need to get a business license first, before purchasing photography equipment, in order to be able to take those items off as business expenses? I am wondering if I can use and claim the equipment I already have as a necessary business expense (you kind of need a camera to be a photographer) or if I have to have a business license prior to buying the stuff. Professionals who have done this would be a great help!