You can store image *name* in the text file or array, and then use it e.g. to load the image from URL. You cannot store anything else than a string or a number in an array. As paulscottrobson suggested, the number can be used to refer to another object UID. But in your case this seems overcomplicated.
If you have a set of pre-defined images, it might be easier to store them as separate animations in a single sprite, label the animations with image names, and then choose one of the images from the list. You could use the "choose" expression e.g. Sprite.SetAnimation(choose("image1","image2","image3")
Alternatively, you can store images as separate frames of a single animation, and then show a random one with Sprite.SetFrame(int(random(Number-of-Frames))