You could do this with an app like https://apps.shopify.com/image-master
It does not automatically add the watermark/overlay when a product is pre-order - but you can easily search for the products that you want to add the overlay to and add the desired text or image overlays. Then when the product is out of pre-order you can go back and remove the overlay.
I would do this / have done for you in the theme code - it will load faster and cost less over the long term.
Here's how I do it:
1. Find the snippet that displays your product images (probably something like product-grid.liquid, or product-thumbnail.liquid, etc).
2. Add the image with html.
3. Set the size / position with css.
You can also use Liquid to show only for certain conditions like new arrivals, on sale, under X price, etc.