Google messenger is a texting app, so your picture messages will be sent via MMS. Your carrier sets the limit ATT is 600kb. Use email for bigger picture files - gmail is something like 20 megabytes.
Why? Because that app will allow you to send your big MMS pix via WiFi....
However, you must consider the other guy, if you send him a big picture, he has to Pay $$$ to download that picture (unless he has an unlimited data plan)