I would like it placed on record that these images in no way excuse the wearing of tights. All tights should be destroyed. However, there are (or, more precisely, were) times when the practice was acceptable.
If all of the following rules are adhered to, tights are permitted:
They are fishnets.
They have no 'reinforced gusset'.
They are seamed.
They are black.
They are worn by a leggy female model any time before 1965.