A photograph of boxes of Tyson Food products bearing labels identifying the contents as [inverted] "Boneless Pork Rectums" originated (as far as we know) in 2007, when it was posted to the Taiwan-based Forumosa message board by a user who described it as a picture "Taken last week outside a local dumpling shop":
The attached picture has appeared now on several image sites on the Internet. I've tried searching to see if this is real, faked, or Photoshopped, but haven't found an answer. If this is real, for what ungodly purpose would this "Product of the USA" be used for?
Tyson declined to verify for us whether the displayed photograph was a genuine picture of one of that company's products, but we see no reason to doubt that it is. Unlike such notorious fictional gag items as "fish assholes," pork rectums (including the inverted variety) are a not uncommon food product, used in such dishes as chitlins (or chitterlins) and vended by many different companies in a variety of countries.
The image was later (quite poorly) altered to make it appear as if the packages bore a McDonald's logo, and an appended rumor held that the product was used in the chain's McRib sandwiches. However, the image was identical to the original and the story of its origin differed when it began circulating: