That's how pictures are sent. In the form of data. But they won't charge you for that if you have unlimited SMS and MMS. Just make sure you don't have nything running in the background, like facebook or some other app.
It's just the way the current cell network technology was designed, it's neither Apple or Koodo's fault in this case. Pictures are sent through the internet as data.
Another thing to keep in mind as you're using an iPhone is imessage uses data. So if you have iMessage turned on, and try to send a picture (or text) you will be charged for data as it is not SMS/MMS at that point any longer.