The photos are a stereo pair. 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.
No, the photos represent different ways of looking at spectral information. The one on the left is brightness from all wavelengths together (monochrome). The one on the right is false color, showing information about various wavelengths and combinations by the color in the image.
This sort of thing is common in remote sensing. Spectral information can tell you interesting things - it is color vision, except the "colors" are not the ones your eyes see.
That being said, I can't tell you what the colors mean. That's why they have specialists.