Portfolio required, and must be able to demonstrate knowledge of studio lighting and programs such as CaptureOne. If successful, you'll be invited to spend some time on set with another photographer to prove your skills.
I applied online. The process took 1 week. I interviewed at iHeart Studios (London, England) in Jul 2017
Interview
Brief discussion about the role followed by a trial shadowing one of the full time photographers on a still life set for a couple of hours. A second discussion before being asked to come back for a full (paid) trial day.
I applied through an employee referral. I interviewed at iHeart Studios (London, England) in Jan 2017
Interview
Very unorganised, wait time was too long, overly informal and management seemed to have no idea what was going on. Waiting to hear back was weeks and decided against the idea in the end.