How can we check the article is copied or not?
Many kind of content checker tool available on internet. Copy Scape is one of paid source to check copied content.
And you can paste some of the article into google to find if it's appeared elsewhere.
There are lots of duplicate content checking tools. You can use them. You can use the following url to find some tools:http://www.techmaish.com/4-free-duplicate-content-checker-tools/
Apart from that you can paste 4-5 lines of your article content into Google search box and you will get the idea about your content.
You can check your Content by Google Copy your Content And Past It in to Google.com with this format "Content Here"
This topic has been discussed at length in several other threads. Please search the forum and if you have a SPECIFIC question, feel free to post a new thread to ask it.