DICOM, a medical imaging format (meta-format? The spec is a beast) supports JPEG2000 compression. There are a lot of DICOM files kicking around, though annoying not every device can write files with JPEG2000 compression, nor can every reader actually interpret them.

I also had a no-name digital camera that inexplicably supported JPEG2000.

Other than that, I’m don’t think I’ve seen it much in the wild.