Seated Male Nude (recto); Sketches of Hand and Boy'd Head (verso)
School of Rembrandt van Rijn (Dutch, 1606-1669)
or possibly Jacob Adriaenzoon de Backer (Dutch, 1608-1651)
or Matthäus Merian, the Younger (Swiss, 1621-1687)
or in the Style of Govert Flinck (Dutch, 1615-1660)