Find all files (-type f) and pass them one at a time to the next command (xargs -n 1) and take the first 8 characters (head -c 8) of the output, only allowing alphanumeric characters (tr -dc A-Za-z0-9) and generate an MD5 checksum (md5sum).
find -type f | xargs -n 1 | head -c 8 | tr -dc A-Za-z0-9 | md5sum