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For copyleft licenses with an acknowledgement clause, how obvious does the notice need to be?

In licenses such as that of libjpeg and freetype, there are clauses like the following:

(2) If only executable code is distributed, then the accompanying documentation must state that "this software is based in part on the work of the Independent JPEG Group".

or:

o Redistribution in binary form must provide a disclaimer that states that the software is based in part of the work of the FreeType Team, in the distribution documentation.

Is putting a notice in a text file in the installation directory enough? Or is a more obvious notice typically needed? For a non-open-source end application, what's the usual way to display these mandatory acknowledgments?