If you're an iconmaker and post your icons publicly, it will most likely be harvested by iconscraper which is taking advantage of the LJ picture feeds.
So if you don't want your icons to be hotlinked, go to Admine Console. Type set latest_optout yes and click on the execute button. Make sure that you are logged into LJ when you do this.
If you run a community, type set for communityname latest_optout yes.