File:Rilke and Klossowska at Chateau Muzot 1923.jpg

Summary
All indications are that that it was published without compliance to US copyright formalities. All indications point to it being in public domain in Switzerland where the photograph was taken and originated - as a non-artistic photograph it is generally not considered copyrightable under Swiss jurisdiction (see Commons:Template:PD-Switzerland-photo and Art. 2 par. 1 of the Swiss Copyright Act).
 * Other information:

According to the HelveticArchives, the photograph was taken in 1922 (see link).

The only intended use of this photograph will be on the "Duino Elegies" article, as Rilke wrote the work and Klossowska was influential in its creation and in Rilke's life at the time.