The idea is simple. When you take photos you almost always want to take with the highest resolution. Because you can not retake the photo. Then there is a problem. Since I think the standard for the highest resolution is a 4:3 box. For my phone its 2592×1944 = 4*648 x 3*648 or a 4:3 ratio . But the screen has a resolution that is 16:9 in resolution.
Then the idea is to have help lines showing a 16:9 box in the phone camera application. You then aim so that the important stuff is in the 16:9 box. Even if the photo will be a 4:3 box.
Here the idea is to implement automatic crop and store two photos. One with the 4:3 resolution which can be printed on paper and a 16:9 resolution perfect for viewing on the TV or phone.
Perhaps the meta data about the position of the 16:9 box could be stored in the larger 4:3 photo. But when viewing on the TV or the phone it automatically crops the image to the right position.
Maybe a default position like in my screen shot could be used. Equal cut on one side as the other.
The inner box is the 16:9 box of help lines. Then the 4:3 box. The actual photo. This is all wrapped up in the phone screen.
Blender 3D which I used for this is an excellent program on Linux for testing ideas.