
So, why not just copy?
Taking their work is intellectual property theft. And that's not okay.
Just because you see it on the internet doesn't mean you can use it without their permission. Artists make a living by selling their work, and copying what they do isn't a compliment — it's taking bread out of their mouths.
If you really, really want to, you can always ask permission. If you're granted permission, ALWAYS credit your original source, and share the results with them.
If you want to work from the painting of a long-dead old master, take it in a new direction, but include the artist in the title. You can call it "Homage to Rembrandt" — or whomever. Acknowledge your inspiration.
Having had to deal with a violation of my own copyrights, I can tell you from experience it doesn't feel good to find someone has copied your work. It just feels like you've been ripped off.

If that is why you paint — as it is for most people who want to make art— you cannot be truly creative if you are just copying someone else's work.
There are so many things to inspire your work, and to provide you with images to draw and paint. You can, for instance:
- Look around your town for interesting buildings
- Sketch people at your neighborhood coffee shop
- Stop on the side of the road to take photographs of roadside landscapes, or bring your easel along and paint a roadside scene
- Draw or paint a self-portrait
- Look at the little, simple things around you, and create simple still life images
Beauty and inspiration are everywhere — you need never be at a loss for something to paint or draw.
Is it the color palette? The handling of the paint? The subject matter? A particular way of framing the composition? Identify it, whatever it is — and try it out in your OWN work.
There is only one YOU in all the world. There is no one else who can say what you have to say, in the way that you can say it.
As you develop your skills, you will — and should — try many things. Learn from everything you see!
Explore! Practice! Fail (it's okay; it's a necessary part of the process)! Discover! Grow!
As you grow, you will find your own visual voice, your style, your spirit, your genius. You will discover who you are as a painter.

Someone else's great photograph is already art. What more can you say about it visually that it hasn't already said?

Take your own photographs.
Make your own still life setups.
Find your own models.
Learn how to make a great composition.
Then paint, paint, paint, and draw, draw, draw.
You will find your OWN voice. Allow yourself to be influenced by artwork you love. But your own artwork? Make it truly your own work. And THEN you will be an artist.
Trust me: the journey is worth it.