  We present a model-independent method of quantifying galaxy evolution in
high- resolution images, which we apply to the Hubble Deep Field (HDF). Our
procedure is to k-correct the pixels belonging to the images of a complete set
of bright galaxies and then to replicate each galaxy image to higher redshift
by the product of its space density, 1/V_{max}, and the cosmological volume.
The set of bright galaxies is itself selected from the HDF because presently
the HDF provides the highest quality UV images of a redshift-complete sample of
galaxies (31 galaxies with I<21.9, \bar{z}=0.5, and for which V/V_{max} is
spread fairly). These galaxies are bright enough to permit accurate
pixel-by-pixel k-corrections into the restframe UV (\sim 2000 A). We match the
shot noise, spatial sampling and PSF smoothing of the HDF, resulting in
entirely empirical and parameter free ``no-evolution'' deep fields of galaxies
for direct comparison with the HDF. We obtain the following results. Faint HDF
galaxies (I>24) are much smaller, more numerous, and less regular than our
``no-evolution'' extrapolation, for any relevant geometry. A higher proportion
of HDF galaxies ``dropout'' in both U and B, indicating that some galaxies were
brighter at higher redshifts than our ``cloned'' z\sim0.5 population. By simple
image transformations we demonstrate that bolometric luminosity evolution
generates galaxies which are too large and the contribution of any evolving
dwarf population is uninterestingly small. A plausible fit is provided by
`mass-conserving' density-evolution, consistent with hierarchical growth of
small-scale structure. Finally, we show the potential for improvement using the
Advanced Camera, with its superior UV and optical performance.
