Image-based social networking service Pinterest has opened its site to all, relaxing its sign-up policy. Previously, any person, who wished to join the website, needed invites to from existing Pinterest users to "pin" online images onto its virtual "boards". Pinterest, which was launched in 2010, became the fastest-growing site ever, passing 10 million users in nine months, the BBC reports.

According to the report, fashion and recipes have quickly become top topics on Pinterest, while number of its users grew hugely over the past year, digital media analytics company Comscore said.

Although Pinterest has tried different money-raising techniques, the company has not yet disclosed a commercial plan.

“They''re one of the main sites that serve the so-called social collectors, people who like to curate information across the web," said an analyst, Darika Ahrens.

“What remains to be seen is what happens if they start to commercialise, how they''re going to do that and if they do it in a way that''s not going to alienate their users,” she added.