Userpics are icons or avatars used to represent yourself, your moods or feelings, your interests, etc. They are displayed in many locations on LiveJournal, including your userinfo page, your journal, the friends view of people who list you as a friend, comments, support requests, and the comments pages of your entries. In certain situations, you are given the option of selecting the userpic you'd like to use, rather than only displaying your default userpic.
To upload your userpics, go to http://www.livejournal.com/editpics.bml#upload. If you are already at or above your maximum allowed number of userpics, the upload form will not display. After you delete enough userpics to bring your total below your limit, you will be able to view and use the upload form.
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The picture must be a .GIF, .JPG, or .PNG. The actual picture can be no larger than 100x100 pixels, and the file size cannot be greater than 40kb. The image file must be on your local computer, or be accessible via a URL.
After entering your username and password, click on the "Browse..." button beside the file box, and find the image on your computer. Alternatively, you can select the URL option and then type in the Internet location of your image. Submit the form, and your default userpic will appear on your journal (as long as the journal style you have chosen supports userpic display), on your profile, and when you make a comment.
To set your default userpic, enter keywords, enter userpic comments, or delete your userpics, go to http://www.livejournal.com/editpics.bml.