A lot of people have asked if we can measure the distance of an object in photo. But I was wondering if we can measure the size of an object in photo. Of course assuming we know everything from sensor size to height of the photographer etc.
Example: If I take a photo of a bird in flight with only sky as background, there would be no objects in the frame to give an idea of size of the bird. So if I could calculate the size to some approximate level, it would be really nice to know.