There is only one file type that uses the .MIFF extension:
Magick Image File
Image format used by ImageMagick, a program used to view, edit, and convert image formats; stores one or more bitmap images, along with any metadata, such as the author, copyright, image color profiles, and comments.
A MIFF file is saved in the platform-independent Magick Image File Format (MIFF) and consists of a header and binary image data section. The header section is made up of key = value combinations that describe the image in plain text. The binary image data section is formatted depending on the class defined in the header, which is either DirectClass or PseudoClass. Also, the data may be Zip compressed, BZip compressed, run length encoded, or uncompressed.
Updated: October 27, 2014