You simply need something along the lines of:
a = imread('my_epicly_awesome_picture.jpg');
EDIT
To clarify, you can call your function like so:
a = imread('tiger.jpg');
%If your input image is RGB and you want grayscale:
%a = rgb2gray(a);
[m, n] = size(a);
[component_num, c] = i4mat_components(m, n, a);