Basic rule - unless you've purchased a royalty-free source (depending on those terms), you cannot redistribute it in whole or in part. If it isn't yours don't share it. Often the time you've spend finding ways around this or that - loopholing - you could have taken steps already to make your own original ;) Approximating a shape with splines is okay. Lifting actual point locations (though perhaps easier) is pushing it. If there's a discernable pattern in the mesh overall that you did that, it's going to appear to be mesh theft and it is (in a sense) if you copied exact point coordinates in a discernable pattern. You could always ask the creator for permission if you're unsure of the stance of a method you're using.

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