  We investigate the positions and source sizes of X-ray solar flare sources
taking into account Compton backscattering (albedo). Using a Monte Carlo
simulation of X-ray photon transport including photo-electric absorption and
Compton scattering, we calculate the apparent source sizes and positions of
X-ray sources at the solar disk for various source sizes, spectral indices and
directivities of the primary source. We show that the albedo effect will alter
the true source positions and substantially increase the measured source sizes.
The source positions are shifted up to $\sim 0.5"$ radially towards the disk
centre and 5 arcsecond source sizes can be two times larger even for an
isotropic source (minimum albedo effect) at 1 Mm above the photosphere. X-ray
sources therefore should have minimum observed sizes, thus FWHM source size
(2.35 times second-moment) will be as large as $\sim 7"$ in the 20-50 keV range
for a disk-centered point source at a height of 1 Mm ($\sim 1.4"$) above the
photosphere. The source size and position change is the largest for flatter
primary X-ray spectra, stronger downward anisotropy, for sources closer to the
solar disk centre, and between the energies of 30 and 50 keV. Albedo should be
taken into account when X-ray footpoint positions, footpoint motions or source
sizes from e.g. RHESSI or Yohkoh data are interpreted, and suggest that
footpoint sources should be larger in X-rays than in optical or EUV ranges.
