How to make a Photoshop action that applies to any image?

I am trying to create a custom action(macro) for photoshop that takes an image that has four smaller images on it(divided evenly into 4 squares) and save them each as their own separate files, e.g., it would save image1.jpg as: image1a.jpg, image1b.jpg, image1c.jpg, and image1d.jpg, each file having one of the four images in it. So far I have been able to crop and save each image through the action I created, but whenever I try to apply the macro/action to a similar image format it just uses the original image that I created the macro on. I guess I am just wondering how to make a macro/ action that will allow me to apply it to all the images I have formatted like this. Thank you so much in advance for any help!