Is it okay to use stock images?
Stock photos are copyrighted, meaning someone owns them. In order to use them legally, you need permission. Such permission is known as a license, a contract that authorizes you to use the image in certain ways. Without a valid license, you cannot use a stock photo.
Is it OK to use stock images for art?
If the artwork is being used in art for your own personal use or enjoyment, the standard royalty-free license would generally be sufficient. However, if you are using images to create artwork that you intend to sell and/or reproduce, you will need to purchase an extended royalty-free license.