Before we move forward, I want to highlight one aspect that's a little confusing about variations. You can have variations, each with their own unique product image. To do this, follow these steps:
In the backend under Variations, you can select an image:
Then, select that variation via drop-down menus; you'll see the image replace the main product image.
This is one of the most useful application variations as you can show people what they're going to get with each variation.