Depending on the size and type of picture, Ebay allows you to "host" a single picture on their site. This is added to the auction when it is created. You will see a place for this.

If you want multiple pictures or use an odd size/format, you can externally link the picture into your auction. This can be done right through the HTML in the auction information on on the auction form, but requires you upload the picture to some space on the net where you can reference the picture through the URL.

I can give you specific instructions on how to do this if you drop me an email.