Plug-in advice needed

Hopefully this is the right place for this…

I’m trying to replace a Zenfolio gallery site. There, I could upload full-res images, sort them in galleries, and have 2 things happen. 1.) A watermark is automatically applied as a layer, not to the image directly, and 2.) It would automatically display them at lower resolutions for loading speed and image protection. This was helpful if someone wanted to buy a digital image, and I could just login, download it myself and have the full-sized, non-watermarked image ready to go.

What is the best way to accomplish this via WordPress?

Thanks