  The Difference Image Analysis (DIA) of the images obtained by the Optical
Gravitational Lensing Experiment (OGLE-II) revealed a peculiar artifact in the
sample of stars proposed as variable by Wozniak (2000) in one of the Galactic
bulge fields: the occurrence of pairs of candidate variables showing
anti-correlated light curves monotonic over a period of 3 years. This effect
can be understood, quantified and related to the stellar proper motions. DIA
photometry supplemented with a simple model offers an effective and easy way to
detect high proper motion stars (HPM stars) in very dense stellar fields, where
conventional astrometric searches are extremely inefficient.
