Dropbox, meanwhile, created a dedicated app for photos called Carousel.

Bloemhoff is confident that through its practices, Climex is not a target for so- called carousel fraud.

A year ago, it shut down a photo sharing project called Carousel and an email app it had acquired called Mailbox.

Norwegian police charged five men on Monday as part of a European-wide probe into so- called carousel fraud related to the European Union's Emissions Trading Scheme.

Britain said last month it would make carbon trading exempt from value-added tax (VAT) in response to a suspected trading scam called carousel fraud.