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The 500px iPhone app had almost a million downloads when it was pulled from the app store. (500px)

A photography app by a Toronto startup is available for download once more after changes to address Apple's concerns that it "featured pornographic images."

"We're happy to announce that our app is back in the Apple App Store," 500px Inc. tweeted around noon Tuesday.

500px Inc.'s "500px for iOS" allows users to share and showcase their images. When it was pulled from the app store on Jan. 22, it had been downloaded almost a million times.

Apple said the app "featured pornographic images and material," that it had received "customer complaints about possible child pornography," and that it was asking the developer to "put safeguards in place to prevent pornographic images and material."

The company maintained that the app allowed only artistic nudity and was set to disallow searching for nude photos by default.

However, it submitted an update for Apple's review that same day.

The new version in the App Store features a "Mature 17+ rating" and a warning that it includes "frequent/intense sexual content or nudity." It also includes a "Report this photo" button to flag questionable material.