Image scaling

I am doing a project in image processing. I have certain images with me so now I am giving these images to the openpose framework and I will get skeleton data from this. But the issue is For example, if u see an airplane in the sky you feel that you can hold in hand but if it comes near to you it will be very big. My need is I have to make this scale has the same. In my project I have skeleton data from openpose which is nothing but vectors so if the person is far from the camera this vector will be small but if he comes near to the camera this vector value will increase so I need to maintain the same scale in the images. so how can I do I am coding in Matlab