The musician and celebrity photographer took the images for the latest phase of the Martini Royale Casting competition to search for the next face of the brand.
"I wanted it to be kinda fun - natural and fun," Adams said.
"I wasn't really thinking about much else other than just trying to make everyone seem quite natural."
He added: "It was quite interesting to make it work, and it was all down to one picture.
"I moonlight as a singer. I've got a book coming out in September called Exposed - sort of retrospective of my photographs."
The representative from the UK in the competition is model Elizabeth Griffiths.
The Ibiza shoot was directed by art director Tom Usher and styled by my-wardrobe.com founder Sarah Curran.
Each of the 28 finalists wore a bikini from the Heidi Klein swimwear brand.
The eventual winner of the contest will appear in a TV commercial and win €150,000 (£120,300).
They will also receive 12 pairs of Christian Louboutin shoes and 12 outfits from my-wardrobe.com.