The ".j2k" extension is used by Joint Photographic Experts Group (JPEG) 2000 files. The JPEG 2000 format uses wavelet-based image compression and stores metadata as XML instead of EXIF data.

JPEG 2000 files can be viewed in most modern image viewers, though they are still not as common as standard .JPG files. While JPEG 2000 files may be saved with a ".j2K" extension, they typically have either a .JP2 or .JPX extension.