GitHub appears to have suspended the JuliaImages organization for as of yet unknown reasons. We have contacted GitHub and are awaiting a reply, but in the meantime installations of packages from JuliaImages or those packages that depend on it will fail. We apologize for the inconvenience and will work with GitHub to restore service as soon as possible.
As a temporary workaround in the meantime, if you have Julia 1.4 or above, you may set the
JULIA_PKG_SERVER=geo.pkg.julialang.org environment variable to opt into the new Pkg Server feature that will be coming in Julia 1.5. Hopefully that can get you up and running again if you absolutely rely on JuliaImages in the meantime.