  Scanning tunneling microscopy (STM) is a fundamental tool for determination
of the surface atomic structure. However, the interpretation of high resolution
microscopy images is not straightforward. In this paper we provide a physical
insight on how STM images can suggest atomic locations which are distinctively
different from the real ones. This effect should be taken into account when
interpreting high-resolution STM images obtained on surfaces with directional
bonds. It is shown that spurious images are formed in the presence of polarized
surface radicals showing a pronounced angle with respect to the surface normal.
This issue has been overlooked within the surface science community and often
disregarded by experimentalists working with STM. Without loss of generality,
we illustrate this effect by the magnification observed for pentamer-like
structures on (110), (113) and (331) surfaces of silicon and germanium.
