I am making a social network application where user will come and share the posts like facebook. But now I have some doubts like lets say a user is just shared a content by coping it from another site and same with the case of images. So does google crawler consider it as a duplicate content or not?
If yes then how I can tell to the google crawler that "don't consider it as a spam, its a social networking site and the content is shared by the user not by the me". Is there any way or any kind of technique that help me.
Google might consider it to be duplicate content, in which case the search algorithm will choose 1 version, which it believes to be the original or more important one and drop the other.
This isn't a bad thing per se - unless you see that most of your site's content is becoming duplicated.
You can use canonical URL declarations to do what you are saying, but i wouldn't advise it.