Finding Percentage of Asymmetry

The project i am working on requires me to calculate the asymmetry of certain objects. I have found the border for these objects and calculated the area and perimeter, but now i need asymmetry. asymmetry is calculated by: #folding the image over its closest line of symmetry; #finding the area of the NON overlapping sections; #find the difference between these areas; #divide by total area; I thought about folding the image over its centroid (??), but i cannot figure out how to do it. If anyone could help me with this i would be most grateful. Thanks!