To respect the privacy of your visitors, it is recommended to include the Matomo (Piwik) Opt-out iframe in your website. This iframe will display to your users a short text and let them opt-out in one click.
To find the code for the iframe, login Matomo (Piwik), then click Administration and then click Privacy.
Here is what the opt-out iframe looks like:
Learn more in the Privacy user guide.