Police said a 64-year-old man found the oil paintings at the rest stop near Ohrenbach in central Germany last month.
He later handed them in to police in the western city of Cologne.
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An initial assessment by an art expert concluded the two framed paintings were originals, police said.
One is a self-portrait by Pietro Belloti showing the Italian artist smiling and dating to 1665.
The other is a portrait of a boy by the 17th-century Dutch artist Samuel van Hoogstraten, date unknown.