You could also go to the Snap FAQs to turn Snap off globally, for all websites. (For best results, clear your cache first.)
But both these options place a cookie on your computer. Whenever you delete your cookies, Snap will be re-activated. If you clear your cookies regularly, or if you cannot accept cookies on your computer for whatever reason, what can you do?
If you use Firefox with Adblock Plus, as I do, just add .snap.com/$script and i.ixnp.com to your Adblock Plus filters.
There are similar options for other browsers. spacecowb0y has been collecting instructions from other LJ users on how to turn off Snap in IE, Opera, Safari, Camino, etc. in this post. I have not verified that any of them work (except for Adblock Plus). But they all seem to have been used successfully by other LJ users.
If you want to turn Snap on, look for the adblocking software on your computer and make sure that snap.com and ixnp.com are NOT filtered out. Also, enable Graphic Previews in your LJ Viewing Options.