And if the person agrees, the agree in e-mail is enough (there isn't a need any of formal document)?

<blockquote class="ipsBlockquote" data-author="yckx" data-cid="5016806"><p>If you want to use an image you find online, ask the copyright holder for permission. This is typically the person who maintains the page,</p></blockquote><br />And if the person agrees, the agree in e-mail is enough (there isn't a need any of formal document)?