Frequently zooming in and out to the same photo, Zhu Ziyi spends half an hour airbrushing her face to make sure that almost every pore is perfect before posting the photo on her different social media accounts to attract likes. For her "picky" roommate, it takes all the time before going to bed to get an ideal photo with a perfect face.

Having been in Paris for five years, Zhu and her Chinese roommate are photo-editing savvies compared with their foreign friends. They are quite good at removing pouches and stains, slimming faces, paling the skin and making eyes big and round.

"They don't have so many apps as we do. Most of my French friends only use filters offered by Instagram," says Zhu, 25, who works at an entertainment company in Paris. She has about 13 such apps on her phone.