Microsoft recently created a neat little tool that attempts to guess your age and gender based solely on a photo. Originally designed to test the company's newly released face detection APIs and sent out to just a few hundred people, the page quickly went viral with more than 35,000 people having tried it out after just three hours.

To try it for yourself, simply visit how-old.net and upload an image of yourself (or find and upload a photo of someone else online).

The tool was built by a couple of developers in just one day and demonstrates the power of machine learning. It's not always accurate - it guessed Mark Zuckerberg's age as 36 when in reality, he's just 30 - but it was just one year off with a guess of 90 for Hugh Hefner (he's 89). I tried tricking it with a photo of a cute koala but the tool didn't fall for it.

The release coincides with Microsoft's ongoing Build conference which got under way on Wednesday and runs through today in San Francisco. 

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