1 cm = 47 pixels and it is easy to find distance between 2 images in pixels..
so you can then convert pixels into centimeter ,like you have 200 pixels of distance then your centimeter will be like ---> (200/ 47) = 4.25 centimeter
int distance = imageview1.frame.origin.y - imageview2.frame.origin.y;
int pixeltoCentrimeter = distance/47;
Happy Coding!!!