Tattooing is a process which is performed by scaring and bleeding of the skin with the tip of a needle and then the injection of a hypodermic paint and provided to keep it in. Both the tattooed and tattooist had been cursed by Our Prophet.
Tattoo pits a permanent scar and becomes a part of the body. The important thing here is that both the tattooed and the tattooist had been cursed by the Prophet. Therefore, it is not permissible to have tattoo or to make tattoo but it does not constitute an obstacle for the ablution as it is not on the skin, it has become a part of the body under the skin.
Henna does not pit a permanent scar on the body; it dissolves by having bath day by day, but drawing a picture or printing something on the body (e.g. drawing the picture of a musician or printing the various catch-phrases in order to indicate the political opinion etc.) are the behaviors which aim to look like different or aesthetic concern. The aim of such behaviors should be considered as changing the creation form of human-beings and also aesthetic concern. The Hadith that states tattooing is not permissible as follows;
Messenger of Allah cursed those who take usury, those who pay it, those who attest it, those who record it, and those who practice tattooing and those who get it for beauty, and those who refuse to give sadaqah and militate against it and those who perform or arrange hulle(*) (Bukhari, Libas/Clothing, 82-87; Muslim, Libas/Clothing, 119)
(*) If a man divorces his wife three times, he loses the right to marry with her again. But if this woman marries with another man and if he divorces her or dies, then the woman can re-marry with her previous husband after the waiting period (the time period determined in Quran) has finished. Some people have arranged “marriage of convenience” by marring with the three times divorced women and then have divorced them after wedding night to make them lawful for their previous husbands. It is called as “hulle”. This behavior is cursed in this narration.