Background Removal To Transparent

I need the background taken cleanly off a set of images and delivered with full transparency—crisp edges, no halos, and the subject perfectly preserved. The primary requirement is a transparent background (PNG preferred), but if you can also supply an alternate version dropped onto a forest-, park-, or mountain-style scene, that extra option would be welcomed.

Please keep original resolution, natural colors, and accurate outlines around hair or intricate edges. Final files should be ready for immediate use in web and print.