Mick Rock shot quite a few pictures of his friend Syd Barrett, during the session from which The Madcap Laughs cover would be taken. I find them all stunning, but this one is my personal favorite. I actually have a copy of this photograph at home, signed by Mick Rock himself. The whole session (and many more pictures) can be found in the "Psychedelic Renegades: Photos of Syd Barrett" book, which I highly recommend. Mick Rock | Psychedelic Renegades
Well, it did take me a while to Google the photo, I went by your description till I found one that resembled it. I’m glad it was the right one.
John Lennon - Imagine alternative photo collages with John and cloud(s) and the uncropped photo of John's head, which appears on the LP's label.
The Rolling Stones - Big Hits: High Tide And Green Grass photos taken by Guy Webster at Franklin Canyon Park, Los Angeles, 1965
This photo session is just out of this world. There's a book called "Bleu Melody" which collates every photo that Tony Frank ever took for this album (cover and gatefold). I don't know how to stress how great it is.