  The Mid-Infrared Instrument (MIRI) aboard the James Webb Space Telescope
(JWST) provides the observatory with a huge advance in mid-infrared imaging and
spectroscopy covering the wavelength range of 5 to 28 microns. This paper
describes the performance and characteristics of the MIRI imager as understood
during observatory commissioning activities, and through its first year of
science operations. We discuss the measurements and results of the imager's
point spread function, flux calibration, background, distortion and flat fields
as well as results pertaining to best observing practices for MIRI imaging, and
discuss known imaging artefacts that may be seen during or after data
processing. Overall, we show that the MIRI imager has met or exceeded all its
pre-flight requirements, and we expect it to make a significant contribution to
mid-infrared science for the astronomy community for years to come.
