TL : DR : The sensor of your camera is not perfect . Those imperfections are present in every photo . They can be used to track your device .
The number of megapixel your phone 's camera has translate to the number of dots in every taken picture . 12 megapixel equals 12 million dots . Every dot consists of intensities of the 3 colors , red , green and blue . Theese intensities are the amount of light that hits the sensor . Due to production tolerances , some areas on the sensor will interpret the incoming light slightly different . As a result , some pixels may be a little too intense or not intense enough . The resulting picture will , in turn , always be either a little bit too bright or too dark on this very pixel . In comparison to noise introduced by other sources , like low light , this pattern will stay the same for every photo taken . With 12 million pixels and 3 colors , the pattern is very likely unique . By taking a number of photos we can find out which intensities stay the same , even with changing of the portrayed content and other noise factors . After we filter those , all that 's left is pattern of brighter and darker spots on a pixel level that can be found in every picture taken by this specific camera . This method stays the same for the lifetime of the camera and gives us a solid way to know if photo was taken by this specific phone . It is not version or vendor specific but specific to every single unit produced . We call the extracted pattern fingerprint because with it your phone can be identified Android users can check out this app that shows them this here:
https://play.google.com/store/apps/details?id=de.fau.camfinger
This isn't really a problem at all to the average DNM user lol