Hub,
I'm not a tech genius by any means, but I am pretty sure that has to do with the resolution and/or file size of the individual pictures. If they are cropped, etc they will automatically be smaller. Also, cell phone pics on average tend to be smaller than those taken with a quality digital camera. Not sure if Nafex itself has any effect when you upload them, though I don't think it does.

Look at file size on some of your pictures and you will see the differences I am talking about. (generally you can hover the pointer over the different files and it will pop up saying how big the file is).