Islam greatly believes in freedom of expression. As such blasphemy in Islam is a subject of intellectual discussion rather than a subject of physical punishment.
The concept of blasphemy is completely alien to the original teachings of Islam. Before the advent of Islam, difference of belief was also a punishable act. They used to punish on matters of belief just as on matters of social crime. This old practice is called religious persecution in history. Islam abolished this practice. The Prophet of Islam declared that personal belief is a subject of discussion and exchange rather than of legal punishment.
If you go through the Quran and Hadith, the only two authentic sources of Islam, you will find that there is not a single Quranic verse or Hadith that gives this kind of injunction which says: Kill the person who commits blasphemy against the Prophet.
The Quran tells us that since ancient times God has sent prophets in succession to every town and every community. It says, moreover, that the contemporaries of all of these prophets adopted a negative attitude towards them.