some author republishes figures or images already published by researchers or world agencies and they are limited to the source citation. Is it sufficient to respect the copyright or they must have the author's permission?
For using a figure in your manuscript from other research papers, you must take permission from the publisher under copyright rules and cite it properly. These days to take permission from the publisher is very easy process.
For scientific safty, I think , it' s useful to tak a permission from authors , but eventually if not possible , a recognising by citation is sufficient.