Proof of Prophethood? I'd like to know what prophethood designates in the Bible and what is the scriptural standard for identifying a true prophet? What I mean is, what if someone today stood up and claimed prophecy? How could we tell of his genuine or imposturous nature? 

Moreover, I wanna know the basis and evidence on which the likes of Joseph, the son of Jacob, in specific, is regarded a prophet of God?
Robert P. Carroll says in 'Prophecy and society', published in The World of Ancient Israel: Sociological, Anthropological and Political Perspectives page 209, the Bible presents so many different, ambiguous and ambivalent stories and treatments of prophets that the modern reader has to admit that the ancient Israelite writers had no clear image of what a prophet is or should be.  

Daniel I Block says in 'My Servant David: Ancient Israel’s Vision of the Messiah', published in Israel’s Messiah:In the Bible and the Dead Sea Scrolls, page 32, there is no evidence within the Old Testament that anyone in ancient Israel understood the office of prophet typologically. Nevertheless, the people seemed to know who their prophets were.  An Old Testament prophet did not necessarily predict the future, but his pious sincerity was accepted by his contemporaries, and he frequently claimed that God was speaking through his words. 

The Bible contains accounts of some of the prophets, either in the books of Kings or books said to have been written by the prophets themselves. However, it appears there were prophets and seers whose books have been lost to us, such as a book of Shemaiah the prophet, mentioned in 2 Chronicles 12:15. 

It appears that prophets could provide quite conflicting messages. Jeremiah is considered a prophet, but in Jeremiah 27:9,14,16,17 he tells the people not to listen to the other prophets, only to himself. He was recommending that Judah submit to the yoke of Babylon. In chapter 28, the prophet Hananiah (son of the prophet Azur) said that Babylon would soon be defeated. He took the yoke that Jeremiah had placed on his own neck to symbolise submission to Babylon, and broke it to demonstrate defiance of Babylon. In the event, Jeremiah was proven largely right, and Hananiah receives only a brief mention as a failed prophet; had events turned out differently it might be the book of Hananiah that we read in the Bible, with Jeremiah relegated to failed status.

Ronald E. Clements says in 'Israel in its historical and cultural setting', also published in The World of Ancient Israel, at page 13, the written form of prophecy can be seen frequently to have altered, and at times markedly transformed, the import of the prophet's original words in the Bible, even at times reversing their warnings or assurance. 

If we define a prophet as someone through whom God spoke, then Joseph was not a prophet, as the Bible does not record God as ever communicating with him.