BookRix

There are a few questions I hope you can answer for me: I have downloaded some free pictures from the internet to use for illustrating my books. I do not wish to plagiarize anyone's work, so I need to know if it okay to do what I have done in a book that I wish to sell to the public. My second concern is the protection of my book. If someone downloads my book, can they just change my name to another, then claim it for their own? I've never dealt with ebooks before so I'm not quite sure how this all works. I will appreciate your help.
Sincerely, relybbert