  Large-field multi-color images of 20 galactic globular clusters are used to
investigate the presence of tidal tails around these stellar systems. Field and
cluster stars are sorted with the help of color-magnitude diagrams, and
star-count analysis is performed on the selected cluster stars in order to
increase the signal-to-noise ratio of their surface density. We study the
overdensities of these stars using the wavelet transform of the star counts in
order to filter the background density noise and to detect the weak structures,
at large scale, formed by the numerous stars previously members of the
clusters. We associate these stellar overdensities with the stars evaporated
from the clusters because of dynamical relaxation and/or tidal stripping from
the clusters by the galactic gravitational field. Most of the globular clusters
in our sample display strong evidence of tidal interactions with the galactic
plane in the form of large and extended deformations. These tidal tails exhibit
projected directions preferentially towards the galactic center. All the
clusters observed, which do not suffer from strong observational biases,
present such tidal tails, tracing their dynamical evolution (evaporation, tidal
shocking, tidal torquing, and bulge shocking) in the Galaxy. The clusters
exhibit different regimes of mass loss rate, detected using the radial density
slope in the outer parts of the clusters. For NGC 5139 ($\omega$ Centauri), we
estimate, taking into account the possible presence of mass segregation in its
outer parts, that about 0.6 to 1% of its mass has been lost during the crossing
(Abridged)
