No, as mentioned earlier, picture texts won't send/receive over wi-fi. They don't count against your data package though, they count against your text package.
If both wi-fi and mobile data are turned on, the phone should switch as needed for the picture messages to send/receive, but sometimes it doesn't. That's why it's best to turn off wi-fi and then turn on mobile data at least until the picture texts are sent/received. A pain, but sometimes you do what you gotta do.
