Blurb doesn't review, edit or monitor books as they come through, and we can't advise on whether it's legal or "safe" for you to use content you've found on the internet or elsewhere. Using copyrighted material without the right to do so would violate our Terms and Conditions.
If you're looking for photos or other content for your book: some artists make their content available for reuse through Creative Commons licenses and similar programs. Public domain material may be available as well. There may be restrictions involved so it's a always a good idea to confirm the license and exact reuse terms for any content you wish to use.
The World Intellectual Property Organization also has some excellent FAQs on copyrighted material under the Using other people's work section.
Remember, the content of your book is entirely up to you, the author. We don't review, edit or monitor content but we will investigate any complaints of copyright infringement.