Using a picture or image in your commercial product if you are not sure of the ownership of the copyright is risky. It can be difficult to clear copyright in images because often you can't locate or identify the owner of the copyright. A first place to look is at the copyright notice. If prepared correctly, it will have the name of the copyright owner and you can track them down to ask permission. That is often not the case, though. If there is no copyright notice and you use the image, you are infringing the copyright if it has been registered. Lack of a copyright notice might let you claim that are an "innocent infringer" but that doesn't completely relieve you of liability - or allow you to continue to use the image. To be safe, find a royalty free image or pay for a license to use an image. Make sure that the license allows you to use the image in the way you want in your book. Using the image in a way not consistent with the license is also infringement.