The biggest threat to Facebook isn’t Google or Twitter.

It’s the out-of-nowhere startup that allows people to do what they like to do on Facebook easier and faster.

What people like to do on Facebook is share and view photos of friends and family.

Facebook is popular because it is the easiest way to do that over a computer.

Where Facebook has a huge blindspot, however, is that it is not the easiest way to share photos of your friends and family over your phone.

It’s too slow. 

Already, startups backed by millions of dollars in venture capital are attacking Facebook’s weakness in this area.

The current leader of this insurgency is an iPhone app called Instagram, which grew from 1 million users in January 2011 to 15 million in December 2011.

Instagram isn’t perfect.  You can’t label your photos with your friends’ names like you can on Facebook, for example.

But what’s great about it is that it is very fast – especially compared to Facebook.

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With the Facebook iPhone app, there are 6 screens a user has to go through before a user can actually take a picture. With Instagram, there is one.

This is a long term problem for Facebook. 

According to Mary Meeker, sometime in the middle of 2013, there will be more people on the Internet via their mobile devices than desktops.

If Facebook doesn’t figure this problem out, it will go the way of Friendster. Friendster lost to Facebook because users found they could do what they wanted to do on Friendster on Facebook with much more speed and simplicity.

Facebook is aware of this problem.  A source familiar with Facebook’s photos team tells us one of its top priorities is “reduce the friction to uploading content” through mobile devices.

They have a lot of work to do.