Actually you need written permission to use royalty free images too. Most stock photos available on the internet come with a license agreement that states how you can use them. Many don't permit commercial use or limit it severely. It is important to carefully check the license before using a photograph, even if you paid for it.Generally website images belong to the person who owns the site you take them from, so be very careful. You need written permission to use any images other than royalty free. I would suggest either take your own photos or source your images from a site like bigstockphoto.com where you can pay for the images.