The oldest image of the Prophet Muhammad is from the late Abbasid period and was produced for a Sunnī audience, although most Sunnīs in modernity have largely become averse to such art.  In Sunnī legal discourses, only a group of Mālikī jurists seemed to permit all types of two dimensional art, while limiting certain types of sculptures, see M. Taqi Usmani, "The Legal Status of Pictures and Photography." 

For depictions of the Prophet Muhammad in medieval Sunnī art, see Wijdan Ali, “From the Literal to the Spiritual: The Development of the Prophet Muhammad’s Portrayal From 13th Century Ilkhanid Miniatures to 17th Century Ottoman Art."

The most informative article on depictions of the Prophet Muhammad is Christiane Gruber “Between Logos (Kalima) and Light (Nur): Representations of the Prophet Muhammad in Islamic Painting,” Muqarnas 26 (2009), 229-262, which is available online.  The first two pictures on this page were reproduced from Google Book's preview of the article, see p. 235, 236. 

Two other images are available to view online through a preview of the book The Legacy of Genghis Khan: Courtly Art and Culture in Western Asia, 1256-1353 (New York: 2002), p. 119, 141.

*Note: I do not own these manuscripts. These low-quality images have been reproduced from the aforementioned sites for educational purposes.  If the owners feel a copyright has been infringed, the images will be removed.