Photographer's rights to photos that have been sold

I am a photographer of commercial aircraft and have been selling original Kodachrome slides to a friend of mine for a number of years. I have not been selling him the publication rights to the photos, rather, I have sold him the slides for his personal collection and enjoyment. There is a large community of worldwide collectors of original airline slides. My friend is now selling the slides which I took (that I sold to him years ago) at an online auction site called http://www.AirlineHobby.com for $10, $15 and over $20 US per slide. Although he paid me between $1 and $2 per slide over 10 years ago, I did not sell them to him with the intention that he would be selling them for profit to other collectors. My question is: do I have any legal rights to stop him from selling the slides that I sold him? What can I do to stop him? Is it within my rights as the original photographer of the slide to restrict his engaging in further commerce with my slides?