Today, the full movies of these stills are available on YouTube:
From Castle of Blood I was able to find the exact location of the film still in question. The woman who is wearing the translucent crinoline and who bares her perky breasts appears to be Sylvia Sorrente (Elsi in the film).
From Succubus I was unable to track the still. However, I was able to get a wider shot. La Reynaud appears to be stripping for a pianist seen from the rear in the back.