The Droste effect is when a product's packaging features the packaging itself.
At my grocery store I could only find three examples: Land O'Lakes Butter, Morton Salt and Cracker Jacks. These packages each include a picture of the package itself and are often cited by writers discussing such pop-math-arcana as recursion, strange loops, self-similarity, and fractals. This particular phenomenon, known as the "Droste effect," is named after a 1904 package of Droste brand cocoa. The mathematical interest in these packaging illustrations is their implied infinity. If the resolution of the printing process -- (and the determination and eyesight of the illustrator) -- were not limiting factors, it would go on forever. A package with in a package within a package... Like Russian dolls.
(via andre)