  A key issue for skyrmion dynamics and devices are pinning effects present in
real systems. While posing a challenge for the realization of conventional
skyrmionics devices, exploiting pinning effects can enable non-conventional
computing approaches if the details of the pinning in real samples are
quantified and understood. We demonstrate that using thermal skyrmion dynamics,
we can characterize the pinning of a sample and we ascertain the spatially
resolved energy landscape. To understand the mechanism of the pinning, we probe
the strong skyrmion size and shape dependence of the pinning. Magnetic
microscopy imaging demonstrates that in contrast to findings in previous
investigations, for large skyrmions the pinning originates at the skyrmion
boundary and not at its core. The boundary pinning is strongly influenced by
the very complex pinning energy landscape that goes beyond the conventional
rigid quasi-particle description. This gives rise to complex skyrmion shape
distortions and allows for dynamic switching of pinning sites and flexible
tuning of the pinning.
