JPEG images have different pixel values across multiple devices

Question

I had noticed that when reading in an identical photograph across devices in the JPEG format, the pixel values do not match up. They are close, but different. When convert

Answer 1

I suppose you should also check if compressed PNGs appear the same way across devices.

http://pngquant.org/

If the answer is yes, then the only thing remaining would be to figure out how to convert programmatically on the phone those images to that same kind of compressed png.