Written permission may not need to be obtained in certain circumstances, such as the following:

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  Public domain works are not protected by copyright and may be reproduced without permission, subject to proper acknowledgement. This includes works for which copyright has expired (for example, any US work published prior to 1923), works that are not copyrightable by law (for example, works prepared by US government employees as part of their official duties), and works expressly released into the public domain by their creators. (Permission would however be required to re-use the final formatted, edited, published version of a public domain journal article, for example, as this version is owned by the publisher.)
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  Open access content published under a CC-BY user license, as well as open access content published under other types of user licenses depending on the nature of your proposed re-use (for example, commercial vs. nonprofit use), may not require written permission, subject to proper acknowledgement. Permissions vary depending on the license type, and we recommend that readers check the license details carefully before re-using the material.
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  Creating an original figure or table from data or any fact-based information that was not previously in figure or table format typically does not require permission, subject to proper acknowledgement of the source(s) of the data.

For any further clarifications, you can submit your query via our online form.