  The electromagnetic form factor of the pion is calculated within the use of
functional formalism. We develop integral representation for the minimal set of
Standard Model Green's functions and derive the dispersion relation for the
form factor in the two flavor QCD isospin limit $m_u=m_d$. We use the dressed
quark propagator as obtained form the gap equation in Minkowski space and
within the Dyson-Schwinger equations formalism to derive the approximate
dispersion relation for the form factor for the first time. We evaluate the
form factor for the spacelike as well as for the timelike momentum in the
presented formalism.
  A new Nakanishi-like form of integral representation is proved on the basis
of the vector Bethe-Salpeter equation for the quark-photon vector with a
ladder-rainbow kernel. The Gauge Technique turns out to be a part of the entire
structure of the vertex.
  In the analytic approach presented here, it is shown that the a large amount
of the $\rho$-meson peak in the cross section
  $e^+e^-\rightarrow \pi^+\pi^-$ is governed by the gauge invariance of
QED/QCD, i.e. by Gauge Technique constructed quark-photon vertex. This
approximation naturally explains the broad shape of the $\rho$-meson peak.
