This program takes one image and composites it over a folder full of images, with user selectable position and transparency.
Supports Mac OS X image formats, drag-n-drop, Quartz Compositing, all kinds of juicy goodies!
Source is available.
What is new in this release:
Five years later, had yet another request for dragging images in directly, and finally decided to make it happen. It does now. Added Sparkle for further updates. Also renames the pictures you are working in, rather then overwriting them, in case such overwriting is accidental. Easier to erase the originals then try and get them back, right?