Never, ever use the word 'by' unless you are referring to an 'edited by' line. Otherwise, just use your name as the author name. Don't believe me? Go to a bookstore or Amazon and look at what's out there.
Just because you can right-click an image or take a screenshot does not mean you have the right to just take it. And do not get me started on wiping off someone else's photographic watermark. Just don't do it. Don't be a jerk.
Yellow is a vibrant color but it is rather difficult to see against a white background. If your cover is mainly white, yellow is a poor choice for author or title lettering unless you outline the yellow in a darker color.