Mok Hay Koon is a self-taught photographer, honing his skills by starting as a photographer assistant in 1987. He subsequently joined The Shooting Gallery Photography in 1993 as assistant to Sebastian Tan.

The company venture into television commercial (TVC) production led him to develop an interest in motion picture. Mok was Director of Photography (DOP) for the company from 1998, but left the company to work as a freelance DOP. Diverse projects from there include McDonald TVC and TV drama series for Oak 3 Film. In 2002 he went back to still photography, working freelance for various big studios in Singapore, before partnering with 2 friends in 2003 to form a small photo studio, a precursor to setting up Greyberry Picture a year later on his own.

Clients include McCann-Erickson Singapore,  Doris Soh & Associates, GMP group , MDIS and jewellery companies such as Tiffany & Co., Lee Hwa Jewellery, CitiGems, Goldheart, Aspial Jewellery ,Mondial jeweller ,Royal Insignia.