background image size

How can I control background image precise size? Is it anywhere some figures?

only thing i found was just using the scale tool on it.

For those who are interested in a easy way to set background images, I made this and the program is easy and free  top,right,front,back Viewshttps://www.youtube.com/watch?v=zEirdBHnKKE&list=UUbYvkgTTFkinOtFrF-cdN0A

It is unbelievable that will be easy. I don't know if you can't tell me.