WORRIED ABOUT COPYRIGHT?
You can sign a painting you did from a book or tutorial, just mention it's from a tutorial or book you followed, the problem arises when people take a picture from an art book and post it and say they painted it.
Imagine if someone took your painting you did and said they did it, but it was just a picture of your painting, that would be a big problem.
When you paint from a picture you took yourself you can sell it and prints without any worry, it's all yours.
If you paint from a tutorial or a book is not a problem either, as long as you use it for your own personal use, just mention the artist or book if you showing it off on the internet.
Just think any of us could come up with an amazing painting we did from a picture we took, or just made it up from memory, and it was very sell able, then someone takes a picture of our painting and sign it as their own, and then make prints and sells them, that is against the law and they could end up in court..and owe you a lot of money...
You can paint anything you want as long as it's for your own personal use, unless it's your own original painting from a photo you took or use public domain pictures, there are a ton of pictures for free you can paint and not worry about copyright, or selling the original or prints of the original, just look up
places like http://www.pixabay.com,
I also find it's so much better when I use a photo for reference only and make changes to make it my own, or paint from my own pictures I took myself, when your a beginner you may do a lot of tutorials and learning books before you can go off on your own, so it's good to understand copyright, I hope that helps..