The size of a picture depend on the details in the picture. Take a picture, move the camera 1/4" and take another picture and the two pictures won't necessarily be the same size.
It's probably just a coincidence that the pictures you're taking now are larger.
Also check the message size limit in your text app (whichever one you use) in menu/settings/mms for a size limit. Call Verizon tech support, get to talk to someone who can give you a definitive answer (ask to speak to a supervisor, level 2 tech support, whatever it takes) to find out what THEIR limit in mms size is. It could be larger or smaller than 1000KB. Set your app's limit to Verizon's limit. (You probably got a refurbished phone. The original owner could have reset that number, and if nothing was wrong with the software it wouldn't have been reflashed, so it would still be set wrong.)