Most people rarely use command line tools which can quickly debug this problem.
Using curl -I -L in various ways can quickly determine if content is showing up as duplicate.
Posting a URL is not a copycat problem, so long as your posting a link which has been indexed. Well not a problem for the actual content owner... This is a problem for copycats, because...
Google treats time stamp of person who posts content first as the owner (first person in time) of that content.
Anyone else who does a copy + repost your content will get a duplicate content penalty, so copycats only hurt themselves... so long as your content has been indexed.
For content which has never been indexed, TechnoBear is correct.