The only way to prevent people from stealing your custom emoticons, is to not use them in conversations with people
Bach_m explained exactly right in that the files are sent to the other persons computer to display them. So sorry, but if it bothers you that much, you'll just have to stop using them
I also made my own set of paint shop pro made emoticons.. and I share it with my friends, and I'm proud that everybody liked my emoticons
I release my emoticons under the copyleft license
the only thing I wouldn't like is that some of them said that they made those emoticons and not me ¬¬ .. but well... they are my friends!..
I think n_nU