How can I find any different objects between two pictures in matlab

After reading two images (a,b), I want to find any object in "b" image that does not exists in the first image "a" and object could be of any shape does not matter, the two images are pictures captured in the same place with the same state of the camera. But could be some differences, I want to have the number of these different objects.

this what i have tried so far

i = imread('camera1.jpg');
j = imread('camera4.jpg');
 a = im2double(i)
b = im2double(j)

f1= ones(3,3)/9;
i1=imfilter(i,a);
j1=imfilter(j,b);

ed1 = edge(i1);
ed2 = edge(j1);

madBlock = mean2(abs(double(ed1) - double(ed2)))

Answer 1

[Image Analyst]

Why are you blurring and running an edge detector???? Not necessary. Just subtract, threshold, and threshold above the noise level. Then call bwlabel()

diffImage = abs(a-b);
binaryImage = diffImage > somethreshold;
[labeledImage, numRegions] = bwlabel(binaryImage);

numRegions is the count of the number of regions that are substantially different.

[Hussein]

Thanks, that worked perfectly!