Yes. You can leave a anonymous comment, or you can use OpenID
or your account with Facebook, Twitter, or Google to create an identity account
with some of the features of a standard LiveJournal account.
If a journal or community is set to allow anonymous commenting, you will be allowed to leave a comment without logging into LiveJournal. A generic userpic will displayed next to your comment, and the name above the comment will say Anonymous
. Once you have submitted an anonymous comment there is no way for you to edit or delete it.
If you have an account with Facebook, Google, Twitter, or another website that uses OpenID, you can use that account to log into LiveJournal when you post your comment. Select your login method from the dropdown list available. If you choose OpenID, you will see a place to enter your OpenID URL.
After you have chosen how to authenticate yourself you may enter your comment as normal and then press "Post comment". You will be taken to the website you chose to authenticate with, and you may be asked to authorize LiveJournal. Once you have done so your comment will be posted according to the journal or community's settings and a new identity account will have been created for you here on LiveJournal.
Caveat: If you login with OpenID, you may need to set
an email address before you are allowed to comment. This is because accounts without a validated e-mail address are treated as anonymous accounts for commenting purposes.