Image comparison with respect to edges

I want to compare two pictures with respect to edges.

I have a slit that moves over lens and camera takes pictures for each step on lens.

To detection of starting point of lens, i want to take pictures continuously and use edge detection to compare with old picture until having a picture with edges.

For example the first picture is completely dark (completely zero on binary) and the next picture has some 1s on binary. How can i compare and tell to program if an edge occurs?

Example picture: http://imageshack.us/photo/my-images/135/filename14.jpg/

Answer 1

[Walter Roberson]

Unless I am missing something (and I probably am),

any(Image(:))

will be true if and only if there are some non-zero elements in Image.

[Can Acar]

Thank you very much, this would be a good idea, i will apply!