I am having the same problem. I selected automatic & manual watermarking, selected a PNG image for the watermark, and set the image sizes on which watermark should appear.

I tried bulk watermarking the images; it ran without errors, but the images don’t display a watermark! I tried uploading a new image; no dice on that either. I’m a little stumped. It seems like a fantastic, simple plugin, but it’s just not working as expected.

Here’s an example: