Ray Batchelor writes:
“The artwork for this postcard is signed by Luiz Usabal Y Hernandez.

It is taken from the Wikipedia entry for “Queer Tango” https://en.wikipedia.org/wiki/Queer_Tango  (accessed 29 March 2016) which includes this quotation from J. Alberto Mariñas:

"The origin of those images, like the origin of the enthronement of tango as a universal fashion, is Paris. They are mostly anonymous pictures of women before the retina of a man one imagines to be complacent with the image of two women narrowing the distance between their bodies, something this dance encourages. One cannot see in them any self affirmation of feminine propriety, but rather, flattery or seduction toward the male spectator.[…]On one hand, Saphic flirtation or outright lesbianism was exercised by valid individuals belonging to circles of artistic luster wherein this was entirely admissible. On the other hand, the cabarets, in their obvious role as vias for sexual escapism, found their place in society. The image of tango between women is to drink from both springs and, from both, some images representing it have been handed down to us."J. Alberto Mariñas, They dance alone…[9]

The link is to a decayed English-language website where the images have vanished: http://www.esto.es/tango/english/enEllas.htm Its Spanish original has fared better: http://www.esto.es/tango/espanol/Ellas.htm  and the image is found there, with others.

Why this image, alone, of all images to illustrate Queer Tango and the section “The History of Queer Tango” in Wikipedia? Why none of the many images of men dancing with each other as well? Is this a function of the much commented on gender bias in Queer Tango with more activist women than men?

I added the "(?)" to the caption, as I suspect the postcard may be earlier than 1920s.”

What do you belive the copyright status of this image to be?
Ray Batchelor believes: “The image is out of copyright.”

The image url:
https://upload.wikimedia.org/wikipedia/commons/f/ff/Tango_NEP_postcard_1920s.JPG