Copying other artists work, a thorny issue.

I was walking past an art stall in the market the other day, and saw a painting which I recognised as an old masters work, under a different name. I was immediatly put off and moved on. The painting was obviously newly painted, and a few questions arose in my mind.

Is ok to copy another artists work and make money off of it?

At what point does it become a copyright issue?

If you start off with another artists idea, and modify your painting can you call it your own?

I was once told that if you change the image by some 60% then it cannot be deemed a copyright issue.

I am sure if I were to copy someone on ' Complete Artist ' work and sell it off as my own, most of us would be rather miffed.

Is it ok to copy other artists work to improve your own style, or discover new techniques.

Just wondering!!