Everyone of us has downloaded an iso file sometime or will download one sooner or later. But, how to check for errors in the downloading process. Probably, the server which you are downloading the iso file will have an .md5 file. Once you have downloaded the iso file, download the md5 file, then type:
md5sum -c nameofthefile.md5
and it will check for errors. Note: the iso file must be in the same directory as the md5 file.