Check the item record
Look for the rights information attached to the particular digital object. Europeana explains that rights statements describe the copyright status of an object and indicate whether, and under which conditions, it may be reused.
Do not infer permission from access
A page that lets you view or download an image does not by itself grant permission to publish it elsewhere. Follow the linked licence or rights statement, including any limits on commercial use, changes or required attribution.
Keep the credit with the image
When reuse is permitted, record the creator or contributing institution, the object page, and the exact rights statement. If the statement is unclear or absent, ask the rights holder before sharing.
This guide is general information, not conservation or legal advice. Check the guidance and rights statement for the specific object you are handling or sharing.