We develop a general
framework for the study of strong Morita equivalence in which C∗-algebras and
hermitian star products on Poisson manifolds are treated in equal footing. We
compare strong and ring-theoretic Morita equivalences in terms of their Picard
groupoids for a certain class of unital ∗-algebras encompassing both examples.
Within this class, we show that both notions of Morita equivalence induce the
same equivalence relation but generally define different Picard groups. For
star products, this difference is expressed geometrically in cohomological
terms.