The I2C2 package computes the Image Intraclass Correlation Coefficient ('I2C2'), a global measure of reliability for imaging studies. The method was described in "Quantifying the reliability of image replication studies: the image intraclass correlation coefficient ('I2C2')" https://doi.org/10.3758/s13415-013-0196-0.
You can install afnir from github with:
# install.packages("devtools")
devtools::install_github("muschellij2/I2C2")