If you have the focal length of the camera and the height of the aircraft then you have the (approximate) scale of the photo. Then you can calculate approximately the length of the object.
eg focal length 100mm flying height 1000 metres then scale is 0.1/1000. Or 1 to 10000.
You measure the length of the object on the photo say 2.4mm therefore actual length is 10000 times that or 24000 millimetres, 24 metres
As has been repeated many times already the longest shipping container is 40' or 12.2 metres or so.