Image Comparision on percentage format

Question

I want to know whether it's possible to comapre images using asp.net irrespective of their format,size and result should be in percenatge format like 80%-90% like that...

Iam comparing two similar images taken from a webcam but when i compared it pixel by pixel ,there is difference in pixels so my program showing those are two DIFFERENT IMAGES

SO I WANT TO GET THE RESULT IN PERCENTAGE FORMAT PLESE HELP ME ON THIS