I had something like this happening when I had the "send & receive frequency" set to 1 minute in Outlook Express.
Think that when I right-clicked on a photo and elected to send as an eMail the "1 minute timer" would expire whilst it was only half gone and send another copy. If you were on dial up rather than broadband this could loop sending multiple copies?
Fix for me was to change the timer to 5 minutes (Tools Options is Outlook Express) and it hasn't happened since.
RC