1)main requirement is to find approximate size of object in image and if possible its distance to camera.
2)Images/Videos comes from different sources/different people.but i can get their camera or device name in most of the cases.
3)For my personal testing I use Nikon p900 camera
4)i sometimes get approximate parameters of object in image like “distance b/w object and person” and altitude of object from person.but its just from their assumption and also they are not provided in all cases.
5)I read your tutorial about “measuring object size” with coin as reference. similar approach of some hidden reference object if possible is ok for me but i leave that part to decide yourself
Examples of images and video can be found here: