Why can't i send picture texts on my iPhone?

I'm trying to send a picture on my iphone 5 but it keeps saying "Not delivered". Anyone else having this problem?

What I would do would be Reset Networking settings, under Settings-General-Reset. The only thing that you will lose is your Wi-Fi passwords will need to be re-entered the first time.

This has cleared up a lot of texting issues (w/ imessage and normal texts.