Costa has previously held senior roles at Ford, Expedia and CBS Outdoor International (now Exterion Media). She will work with employees across PhotoBox's four brands, including Moonpig and Sticky9.
She is charged with leading the company's international expansion and driving the business forward while "preserving its start-up culture".
Costa told HR magazine she looked forward to the challenge of being the first group HR director across the four brands.
"Having a role across four companies and three countries means there are challenges around culture," she said.
"But it's great to be able to help a successful company grow while keeping the personal feel. We sell a personal product, of which I was an early adopter, so that's an important goal."
Photobox group CEO Stan Laurent welcomed Costa's experience in media, internet and manufacturing businesses.
"These will prove invaluable for our diverse and growing organisation. I have no doubt she will make a significant contribution to the group and help us excel as we continue to expand and strengthen our teams," he said.