Select which Imagecache image is used

Is it possible to use an imagecache derivative as the base for the zoomify, instead of the original imagefield image?

I'm currently using image, but will soon switch to imagefield. One reason is that I want to watermark some images. So when I view the node I'd see a small version of the image without watermarks, but when zooming in I'd like to see the watermarked version (ie the imagecache file), rather than the file that was originally uploaded.

Thanks, David