This workflow uses Watermarker 2's AppleScript support to batch process images with pre-configured presets from the app.

More info on Watermarker 2:

Watermarker is a professional tool for branding images with a wide varitey of watermark types. No stone was left unturned when it came to overhauling the original Watermaker. It was necessary to completely re-write Watermarker from the ground up using the latest technologies to accomplish Watermarker's ambitious feature set. Thanks to these new technologies, not only is Watermarker fundamentally faster but it also has exciting new features like the Photo Editing extension that allows you to watermark images from other apps — e.g. Mail.app. Whether you are interested in promoting your brand or business logo on website images, or just simply trying to restrict unauthorized use of your photos, Watermarker is the app to use.