My original tumblr post was here. This cropped paperback cover image was first posted by Pulp Desire with the following explanatory text:

The Female Man

Bantam Books Q8765

Published 1975

Cover Artist: Morgan Kane

“Across the boundaries of alternate worlds, beyond all sexual barriers, comes the only kind of man there is.”

The explanatory text oddly omits that the author of the underlying book was Joanna Russ. Here is the uncropped cover, found at Ravishly.com.

The original image comes to us via Science Blogtion.