Hacham Ovadia Yosef ruled that taking fingerprints is forbidden on Shabbat, as it falls under the prohibition of writing. By the same token, taking a photograph would also violate this prohibition.
The Torah prohibition of writing on Shabbat is violated by writing two or more letters, though writing even just one letter is forbidden Mi’de’rabbanan – by Rabbinic enactment. Hacham Ovadia notes that if one writes on Shabbat one letter and there is carbon paper underneath such that the letter appears on two different pieces of paper, one has transgressed the Torah prohibition, since he produced two letters.
It is forbidden on Shabbat to write with one’s finger in the condensation of windows, though making a line, without forming letters, is permissible.
Hacham Ovadia ruled that if one smokes a cigarette on Yom Tob, and as the fire burns the cigarette it erases the name of the company printed on the cigarette, this does not violate the prohibition of erasing on Yom Tob. This kind of erasing would, in principle, be forbidden only Mi’de’rabbanan, and one may perform an act on Shabbat or Yom Tob that would inadvertently result in an unintended violation of a Rabbinic prohibition. Therefore, erasing letters on a cigarette by smoking does not violate the prohibition of erasing on Yom Tob, as the erasure is unintended. (It goes without saying that one should in any event refrain from smoking because of the damage it causes to one’s health.)
Writing on Shabbat with one’s weaker hand – the left hand, if one is righthanded – does not violate the Torah prohibition of writing, but is nevertheless forbidden Mi’de’rabbanan. Hacham Ovadia ruled that if one types with a typewriter on Shabbat, then he violates the Torah prohibition of writing regardless of which hand he uses, as long as he types in the normal manner of typing.
One should not make letters on Shabbat in a liquid that spilled, even though the shape of the letters will last for only a very brief moment.
It is entirely permissible on Shabbat to make the motion of writing letters in the air, since this does not create any form of the letters, even temporarily.
Writing on Shabbat with ink that disappears after a period of time is forbidden Mi’de’rabbanan, and does not violate the Torah prohibition of writing. Therefore, Hacham Ovadia advised that doctors who need to write prescriptions or other important medical information on Shabbat for a seriously ill patient should use the "Shabbat pens" with temporary ink, in order to avoid the Torah prohibition of writing on Shabbat.
Summary: Taking fingerprints or photographs on Shabbat is considered writing and thus forbidden. It is forbidden on Shabbat to write in the condensation that forms on windows, or in liquid, even though the letters remain for only a brief moment. It is permissible to make the motion of writing in the air. Doctors who need to write prescriptions for seriously ill patients on Shabbat should, if possible, use the special "Shabbat pens" that have temporary ink.