  Intracluster Light (ICL) provides an important record of the interactions
galaxy clusters have undergone. However, we are limited in our understanding by
our measurement methods. To address this we measure the fraction of cluster
light that is held in the Brightest Cluster Galaxy and ICL (BCG+ICL fraction)
and the ICL alone (ICL fraction) using observational methods (Surface
Brightness Threshold-SB, Non-Parametric Measure-NP, Composite Models-CM,
Multi-Galaxy Fitting-MGF) and new approaches under development (Wavelet
Decomposition-WD) applied to mock images of 61 galaxy clusters (14<log10
M_200c/M_solar <14.5) from four cosmological hydrodynamical simulations. We
compare the BCG+ICL and ICL fractions from observational measures with those
using simulated measures (aperture and kinematic separations). The ICL
fractions measured by kinematic separation are significantly larger than
observed fractions. We find the measurements are related and provide equations
to estimate kinematic ICL fractions from observed fractions. The different
observational techniques give consistent BCG+ICL and ICL fractions but are
biased to underestimating the BCG+ICL and ICL fractions when compared with
aperture simulation measures. Comparing the different methods and algorithms we
find that the MGF algorithm is most consistent with the simulations, and CM and
SB methods show the smallest projection effects for the BCG+ICL and ICL
fractions respectively. The Ahad (CM), MGF and WD algorithms are best set up to
process larger samples, however, the WD algorithm in its current form is
susceptible to projection effects. We recommend that new algorithms using these
methods are explored to analyse the massive samples that Rubin Observatory's
Legacy Survey of Space and Time will provide.
