Upon downloading Trisquel you should find an MD5 and GPG link. Download the md5 file by:
right-clicking the *.md5 file,
clicking Save Link As (or similar, depending on what web browser you're using), and
saving the file in the same folder that you saved the ISO or torrent file.
GNU/Linux users

Open your Terminal program and cd to the directory that you downloaded the files to. For example, if you downloaded the files to your Downloads directory then type:
cd Downloads
md5sum -c trisquel_7.0_amd64.iso.md5You need to replace trisquel_7.0_amd64.iso.md5 with the name of the *.md5 file that you downloaded, depending on what edition you selected.

If all went well then you should receive the following output:
trisquel_7.0_amd64.iso: OKCongratulations! You can now proceed to install Trisquel.