Sometimes I have to send a pic from my phone to my computer and then upload it to OG, My phone then has options as to how big to make the photo and I have to select a size under 2 MB so that OG will accept it. Im sure other people have other methods as my pics are always small and sideways.
I think maybe some people have different accounts with OG and can publish bigger pics but I'm just guessing there, I really dont know how they do it.