The timing of the upgrade is probably just a coincidence. But the default messaging app might have changed.
All carriers have a very small data limit on SMS/MMS messages (600-1000 KB).
Some messaging apps will silently resize your pictures down to something small in both pixels and compression. Some (most?) messaging apps will not do this, making you do it your self.
Many of the third-party instant messaging services, like WhatsApp, use a bigger data limit, but both the sender and receiver need to be using the same service and app.