Magento 2: How to add different watermark based on Vendor?

I have a multi-vendor setup on my site and based on per vendor products, I want to apply a watermark. By default, Magento applies watermarks on all the products based on the website/ store.
Can anyone tell me how to customize the watermark functionality or point me which file I should extend? I have my custom table from where I want to get the watermark images.