  In this perspective article, we discuss the challenges of imaging assemblies
of particles in three dimensions. Starting from a brief motivation for the
investigation of particulate materials, we provide an overview of experimental
approaches developed for imaging particles. We list the challenges and existing
solutions associated with X-ray tomography, one of the standard methods to
study statics. Subsequently, we discuss challenges and opportunities arising
from emerging new techniques such as radar tracking and `smart' tracers for
exploring granular dynamics. We close with a tentative view on the outstanding
problems and potential solutions in the future.
