What percent needs to be changed on an item before it is copyright infringement?

Answer 1

No matter what you have heard (10%, 300 words, 3 pages, etc etc) there is no set amount of a copyrighted work that can be used before an infringement exists. Each instance is judged on a case-by-case basis.

Answer 2

There are no hard and fast rules on this; the law is intentionally vague. Copying an item directly is infringing on the rightsholder's right to copy, and changing an item is infringing on the rightsholder's right to create derivative works.

Answer 3

Unfortunately there are no hard answers on this in the law; the US Copyright Office explains it this way:

To be copyrightable, a derivative work must differ sufficiently from the original

to be regarded as a new work or must contain a substantial amount of new

material. Making minor changes or additions of little substance to a preexisting

work will not qualify a work as a new version for copyright purposes.

Because preparation of a derivative work is one of the exclusive rights of the copyright holder, you may wish to address the disposition of rights in the resulting work in your licensing agreement.

For more information (if you are in the US) see Circular 14, linked below.