in resources/asciidoctor/lib/copy_images/copier.rb [47:62]
def find_source(block, uri)
to_check = roots_to_check block
checked = []
while (dir = to_check.shift)
checked << block.normalize_system_path(uri, dir)
return checked.last if File.readable? checked.last
next unless Dir.exist?(dir)
to_check += subdirs(dir)
end
log_missing block, checked, uri
nil
end