When is considerably altered code still under copyright.

That is a matter for an IP lawyer and will almost inevitably vary between jurisdictions. If you go down this route you and your client should take professional legal advice (which this post is not, FTAOD)

Which open source licences allow this approach?

AIUI, the BSD licence will allow you to change the code in any way for any purpose and to any degree you so choose. What it does not do is allow you to claim copyright for works which you have not created. Even if the code is released as public domain you cannot do that. eg. I cannot take Newton's Principia and claim copyright for it even though it is now in the public domain. I am not aware of any licence which will allow someone to claim copyright for something which they haven't written and nor would I expect anyone to release code under such a licence even if it did exist. If I annotate or edit Principia I can copyright my changes but not the original work.

In your shoes, I would point out to the client that they can either have the work without copyright transfer or that they can have it with but in the latter case it will cost them substantially more because you will not be able to base it upon the works of others.

But again, seek professional advice.

In reply to Re: Open source code and copyright by hippo
in thread Open source code and copyright by LanX

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