"We want people to know that our original shows are produced by HBO for HBO," said Caroline Wong, the company's director of marketing communications.
Although the channel has been airing in Thailand for the past seven years, it was only two years ago that it started focusing on its own movies "to differentiate ourselves from everyone else", according to Wong.
HBO's original programmes include global smash hits Sex and the City, Six Feet Under and Band of Brothers.
"We want to increase our noise level, especially in the Thai media," Wong said, adding that HBO's search had focused on agencies strong in media relations.
Image Impact will also be responsible for promoting blockbusters carried on the channel. "Over the year, we pick huge titles like Shrek and Harry Potter and the Philosopher's Stone, and we need them to work with the press to create excitement," she added.
Image Impact clinched the retainer contract following a four-way competitive pitch against undisclosed rivals.