Last month in Paris, developer Antoine Morcos received an unexpected email: Facebook Inc. said it was cutting ties with his photo-sharing application, Vintage Camera.

Mr. Morcos, 31 years old, instantly lost nearly half a million registered users who only accessed Vintage Camera through the social-networking site. Facebook, without being specific, said too many users had complained about Vintage Camera, said Mr. Morcos. He appealed, arguing his app fielded less than three complaints for every 1,000 photos shared, but Facebook didn't budge.

"I was really shocked," Mr. Morcos said. "Users were sharing as much as 6,000 photos per day on Facebook; now access is blocked."

Vintage Camera, which competes with Facebook's Instagram app, is one of a growing number of third-party apps that have been blocked by the social network recently.Is Facebook Pushing Developers Into Paying For Participation [online.wsj.com]

Developers say the crackdown is an attempt to stifle applications that compete with Facebook-owned services or part of an effort to get developers to pay for ads on Facebook.