  We present feasibility studies to directly image stellar surface features,
which are caused by magnetic activity, with the Very Large Telescope
Interferometer (VLTI). We concentrate on late type magnetically active stars,
for which the distribution of starspots on the surface has been inferred from
photometric and spectroscopic imaging analysis. The study of the surface spot
evolution during consecutive rotation cycles will allow first direct
measurements (apart from the Sun) of differential rotation which is the central
ingredient of magnetic dynamo processes. The VLTI will provide baselines of up
to 200 m, and two scientific instruments for interferometric studies at near-
and mid-infrared wavelengths. Imaging capabilities will be made possible by
closure-phase techniques. We conclude that a realistically modeled cool surface
spot can be detected on stars with angular diameters exceeding ~2 mas using the
VLTI with the first generation instrument AMBER. The spot parameters can then
be derived with reasonable accuracy. We discuss that the lack of knowledge of
magnetically active stars of the required angular size, especially in the
southern hemisphere, is a current limitation for VLTI observations of these
surface features.
