Why is my photo showing up as a black square when I post it to instagram?

I have an iphone 4 with the latest version of instagram and i have been trying to put up a photo for a few days but it always shows up as a black square.i've already tried restarting my phone and reinstalling the app. Any ideas on how to fix it?

Did you take the shutter cover off of your phone. The new ones come with a little camera cover that you have to go in with a knife n take out