You're right, I was referring to the one in the inspect screen. And 370x608 seems right.
So, 500x1080 is the official size? I was looking for it but couldn't find it. Where does it stated?
Viewing post in Full Body Image Ratio
370x608 I got by opening the code and looking at the size of the panel where the images are put. Likewise, 500x1080 I got from looking at the game's images that it uses and looking at their size. I do not know that there is actually any official size. I simply know that 500x1080 is the size the game currently chooses to use for its own images.