miff(4) on Linux
The text b80451d1dcb5, as Debian 3.0 (Woody) shipped it.
Magick Image File Format is a platform-independent format for storing bitmap images. MIFF is a part of the ImageMagick toolkit of image manipulation utilities for the X Window System. ImageMagick is capable of converting many different image file formats to and from MIFF (e.g. JPEG, XPM, TIFF, etc.).