@sources, i'd be extremely grateful if you clarify how it is possible to perform your recommendations.

"Using someone else’s photos or text without linking to the original source" -- I have bought a printed postcard or picture at antiq shop. there is no artist credited there. the card/photo was released, for example, in 1900, 1920, 1950 year...
imagine, I created a scan and I want to share a piece of my country's history. this material cant be 'googled out' and obviously is not the part of modern internet. due to the date of original publication, the copyright is expired and rights for a certain document are liberated, i.e. belong to all of the people, not to the artist or his living relatives (as wikipedia states this).

what 'links' to what 'sources' you request me to add to my (possible) post ?!?!