Answered my own question.
for anyone else that needs the info
Steps to enable or disable mobile data on your Samsung Galaxy S III
You may wish to disable mobile data to improve battery life or while troubleshooting connectivity issues.
Yep, picture messages won't send/receive over wi-fi, they require a data connection. They don't count against your data package, though, they count against your text package.
You can also enable or disable mobile data with the notification menu that slides down from the top of your screen. There is a button there between mute and screen rotation, and sometimes it gets hit accidentally. My husband wanted to throw his phone across a room when he turned his data off and didn't even realize he could do that.