So when is it ok to copy?

A few thoughts about the subject of copying other Artists work.
First it is wrong to copy and if you are doing it then you are doing the wrong thing and stealing the image and intellectual property of another Artist, even if they are dead.
If you copy paintings out of an Art book check the front and you will see it is copyrighted and you need permission to copy it otherwise you are breaking the law.
Other than at Art school as a student, I can find no other legitimate reason for an Artist to copy another’s work. Yes you can come up with a thousand reason why you do it, but it is wrong.
So when is it ok to copy?
When you draw the image from nature or life and use it in your paintings.
When you take the photo of the scene and you use it, your own photo or you use photos from copyright free places, I still find this a very grey area.
If you are copying another Artists work and then selling it without their express permission in writing and also acknowledging them on the painting, then you cannot do that, it is wrong.
If you are coping one of the masters and then you are going to sell it, you must first try to get permission from the owners of the copyright of that painting, if copying from a book then you need permission of the publisher and then also acknowledge it is a copy on the painting by the master. Something like, “ after Picasso.” above you signature.
I had one Artist want to put a portrait of Elvis into a Gallery I was involved with and I said only after you get permission to use his image. I told them to email Gracelands to ask for permission to use the image and then print off the email, even if they do not get back to you, your intention was to get permission.
A photographer told me that he really liked a painting in a Gallery I was consulting for and he wanted to take a photo of the painting and then he would get it printed onto a canvas and hang it in his home. I told him, no, you cannot do that without the written permission of the Artist, he said but no harm is done, I told that he was stealing the image of the Artist, if he wanted to photograph the painting, then talk to the Artist and pay for the use of their image, he got upset with me and left.
I remember one exhibition I was in a long ago and an author came up to me and said he loved one of my paintings and asked if he could take a photo of the work and then use it on the cover of his book, I asked him if he was going to buy the painting, he said no. 
I asked him he would pay a fee for using my image he said no.
I then said in front witnesses, no you cannot use my image in any way at all, he got upset and said how it would be great promotion and exposure  for me, I still said no, I cannot buy food with promotion and exposure, he didn't use my image.
We must respect the owners of the image.
This is such a touchy subject and I always wonder why? 
If you are a creative original Artist then this issue would never arise as you would be always searching for your particular original motif not to copy what something someone else has painted, that is theft.
People who copy and take credit for the work only show their true nature and character and their total lack of original thought. They are to be pitied not railed against because in their own heads they have already convinced themselves that they have done nothing wrong. As one woman said to me who had blatantly copied a Gustav Klimt painting, I changed the face of the girl so now it is my own original work, I said no, you stole the image.
If this has happened to you, remember life always sorts them out, so help life along and get legal advice. 
What goes around comes around.