Recently opened at the Detroit Institute of Arts: Foto Europa: 1840 to present.

Foto Europa: 1840 to Present — Events & Exhibitions at The Detroit Institute of Arts

It's a fine though small exhibit, mostly from the DIA's own collection, centering on German, French, and English practitioners, featuring 2-8 prints per artist. Some of the luminaries represented:

Herbert Bayer
Hannah Hoch
Julia Cameron
Andre Kertesz
Moholy-Nagy
Brandt
Tillmans
Frank
August Sander (nice selection incl "Young Farmers")
Cartier-Bresson
Ilse Bing

Of local interest (Detroit-themed): Vermeulen, Marchand & Meffie