Ray Batchelor writes: A YouTube clip showing that it IS Tango: https://youtu.be/AzHyXhTlT90
A summary of the film here: https://en.wikipedia.org/wiki/The_Conformist_%28film%29
This is a much-reproduced still taken form the film. This image is black and white while the film itself is in colour
I find this image interesting because it has so many layers. I have not watched the film (and would love to hear from those who have) but as I understand it, the dance is intended to show an alternative to the conformism demand of people by the fascist regime. Why was such an idea attractive to Bertolucci in late 1960s post-war Italy? The dancing is perfunctory, but an unusual example of a women couple dancing tango on film.
Ray Batchelor believes: “The image is out of copyright.”