imgur is most used image host on reddit.com and this extention is very handy for us redditors. The url format is http://i.imgur.com/XXX.jpg or .png .gif etc. where xxx is random name of the image. ie.: http://i.qkme.me/358582.jpg
OpenID is service that allows you to log-on to many different websites using a single indentity. Find out more about OpenID and how to get an OpenID enabled account.