  Measurements of the deep-inelastic scattering (DIS) of leptons and nucleons,
$e+p\to e+X$, allow the extraction of Parton Distribution Functions (PDFs)
which describe the longitudinal momentum carried by the quarks, anti-quarks and
gluons that make up the fast-moving nucleons. While PDFs provide crucial input
to perturbative Quantum Chromodynamic (QCD) calculations of processes involving
hadrons, they do not provide a complete picture of the partonic structure of
nucleons. In particular, PDFs contain neither information on the correlations
between partons nor on their transverse motion. Hard exclusive processes, in
which the nucleon remains intact, have emerged in recent years as prime
candidates to complement this essentially one dimentional picture. The simplest
exclusive process is the deeply virtual Compton scattering (DVCS) or exclusive
production of real photon, $e + p \to e + \gamma + p$. This process is of
particular interest as it has both a clear experimental signature and is
calculable in perturbative QCD. The DVCS reaction can be regarded as the
elastic scattering of the virtual photon off the proton via a colourless
exchange, producing a real photon in the final state. In the Bjorken scaling
regime, QCD calculations assume that the exchange involves two partons, having
different longitudinal and transverse momenta, in a colourless configuration.
These unequal momenta or skewing are a consequence of the mass difference
between the incoming virtual photon and the outgoing real photon. This
skewedness effect can be interpreted in the context of generalised parton
distributions (GPDs). In this proceeding, we examine typical measurements from
HERA and prospects for COMPASS at CERN, that can bring new insights on the
quarks/gluons imaging of the nucleon.
