The native Camera app has received an update on Windows 10 Mobile. The update takes the app version to 2016.722.11.0. While the update doesn’t bring any visual changes if you go to settings you would be able to notice something new.
There is a new option “Image Size for main camera” which has a drop-down option. On devices like Lumia 950 / Lumia 950 XL it should allow to change the resolution for capturing images. But on other devices like Lumia 640 / XL it just allows one to see the image size when you change image Aspect ration in settings. May be with future updates it allows changing image size on other devices too.