How to Know the index of picture is showing on Sprite

Hi all,
I’m making a simple spaceship shooting game, some time when the laze(Sprite_Shoot) collide with the asteroid I change the image of asteroid sprite to the random next picture in the picture list.

Picture list of Asteroid sprite

Now I need to know the index or name of the picture is showing on the Asteroid Sprite to make behavior when it collides with the laze again.
How can I do that, thanks in advanced