Kaph is one of the Hebrew letters most easily confused with a close neighbour in ordinary handwriting, in this case Beth, discussed elsewhere in this atlas: both letters share a similar squared outline, and Jewish scribal law fixes the distinction on the shape of the trailing lower-right corner, which Beth draws with a sharp right angle and Kaph draws rounded, a difference small enough that a sofer must check it deliberately rather than trust it to come out correctly by habit.
Getting the distinction wrong is not a minor slip: a Kaph written to look like a Beth, or the reverse, changes the word it appears in and can invalidate the passage under Jewish law governing Torah scrolls, tefillin and mezuzot. Kaph is also one of five Hebrew letters that take a separate, elongated form at the end of a word, a final Kaph, discussed at length elsewhere in this atlas as its own entry; that distinction between medial and final shapes is unrelated to the Beth-Kaph confusion, since both the ordinary and the final form of Kaph must each be kept clearly apart from Beth's single, unvarying shape. Kaph's Hebrew name, meaning the palm of the hand, is itself old enough to predate the square script entirely, carried over from the earlier palaeo-Hebrew writing that Jewish tradition holds the Aramaic-derived alphabet replaced after the Babylonian exile, discussed elsewhere in this atlas, so the letter's meaning and its current outline come from two different eras of the same alphabet's long history.