Identifies an NSNumber object containing a boolean that indicates whether the image uses progressive encoding.
Used only for JPEG files. It’s set when reading in and used when writing out.
Available in Mac OS X v10.4 and later.
Declaration Syntax Version Information- Available in Monobjc Bridge: 10.6 (For Mac OS X 10.6 and later), 10.5 (For Mac OS X 10.5 and later)