For those of you unfamiliar with the photo social network known as Instagram, it’s basically a cross between Flickr and Twitter (with a dozen plus photo filters to help spice things up).

Despite being only 7 months old and operating underneath Facebook’s and Flickr’s shadow, Instagram has become a blockbuster hit with the site now adding over a million users per month!

Co-Founder Kevin Systrom revealed Instagram’s latest stats upon TechCrunch Disrupt, and announced that the platform now boasts 4.25 million users who are uploading an average of 10 photos per second.

What’s incredible about Instagram’s growth is the fact that users can only access  and upload photos via an iOS device (or rather the iPhone as Instagram lacks an iPad app).

Note: Instagram is rumored to be working on an Android app, although they refuse to give an ETA on when it will appear upon Android Market.

Instagram’s biggest rival (aside from Flickr) is probably Path.com, whose iOS only strategy has not yielded similar results.

Have you tried Instagram? If so, what are your favorite filters? Also do you think Instagram could challenge Flickr in the future?