  Understanding the mechanisms behind high-$T_{c}$ Type-II superconductors (SC)
is still an open task in condensed matter physics. One way to gain further
insight into the microscopic mechanisms leading to superconductivity is to
study the magnetic properties of the SC in detail, for example by studying the
properties of vortices and their dynamics. In this work we describe a new
method of wide-field imaging magnetometry using nitrogen-vacancy (NV) centers
in diamond to image vortices in an yttrium barium copper oxide (YBCO) thin
film. We demonstrate quantitative determination of the magnetic field strength
of the vortex stray field, the observation of vortex patterns for different
cooling fields and direct observation of vortex pinning in our disordered YBCO
film. This method opens prospects for imaging of the magnetic-stray fields of
vortices at frequencies from DC to several megahertz within a wide range of
temperatures which allows for the study of both high-$T_{C}$ and low-$T_{C}$
SCs. The wide temperature range allowed by NV center magnetometry also makes
our approach applicable for the study of phenomena like island
superconductivity at elevated temperatures (e.g. in metal nano-clusters).
