Why can't I send pictures on my iPhone 4? - 1

I want to send a picture through text message on my phone but the little circular camera option next to the box where you type your text isnt letting me click it. Does any one know what I can do?

My iPhone is unlocked using tmobile and I just upgraded to iOS 6.1. Not sure if that helps but I've not been able to send picture messages through texting for the longest.

Make sure MMS is on in your message settings.