What is the ruling on placing a black dot on a child's forehead with the intention of warding off the evil eye, and is that considered shirk (polytheism)?

First: It is not permissible to believe that the black spot on the forehead repels the evil eye, as there is no Sharia-based or scientific evidence for that. Whoever believes that something that is not a cause is a cause has committed polytheism (shirk), and amulets of all kinds are shirk.

Second: Placing a black spot on a child's forehead to alter their appearance and diminish their beauty in order to reduce their susceptibility to the evil eye is permissible. This falls under the category of concealing beauty, and the intent is not that the spot itself repels the evil eye.

Third: There is no harm in tapping the spot in a picture, as long as it is not believed that it repels the evil eye.