Social media use of legally published images in social media (re-post)
Images can be used if both the copyright holder of a photograph and right holders of a photograph subject according to the Copyright Act have given permission for publishing or if there are other statutory grounds. In this case, the images have been legally published and may be used in accordance with the terms and conditions of social media.
Further use of legally published images in social media in other ways
Pictures may be reproduced, as permitted by the Copyright Act, if they have been made public. Publication requires that a picture has been made available to the public, that is to say, that the picture has been published with a public label.
Sharing material with images made by others on social media
Social media terms require such extensive rights that you can share your own material, CC-BY-licenced material, or in accordance with other permission allowing use social media.
Optimising further use of your own material
If a large number of users of your own material is desired, the CC-BY-license should be preferred, which also allows sharing the material on social media by other users.