  We argue that study of the cross section of coherent photo(electro)
production of $\rho,\rho^{\prime}, ...$-mesons provides an effective method to
probe onset of black body limit(BBL) in the soft and hard QCD interactions. We
illustrate the expected features of the onset of BBL using generalized vector
dominance model(GVDM). We show that this model describes very well $\rho$-meson
coherent photoproduction at $6 \leq E_{\gamma} \leq 10$ GeV. The advantages of
the process of coherent dijet production and hard diffractive processes in
general for probing the onset of BBL and measuring the light-cone wave function
of the photon in a hard scattering regime where decomposition over twists
becomes inapplicable are explained. We argue also that the regime of color
fluctuations manifests itself at intermediate energies in exclusive and
semiexclusive photoproduction of vector mesons and that the color
transparency(CT) should reveal itself in these processes at $Q^2$ of the order
of a few GeV$^2$.
