Difference between Images and if statement

    a = imread('Image1.jpg');
    b = imread('Image2.jpg');
    c = imshowpair(a,b,'diff');

I have this variables now I want to do something like this:

    If c==true
        haveDifference = true;
    else
        haveDifference = false;
    end

This don't work it's says it's false even they have difference!

[per isakson]

Doc says:

   h is a handle to the HG image object created by imshowpair.

i.e. c is not a logical variable