The second-most notorious trading card in history (after the infamous Fleer "f*ck face" baseball card) is the C-3PO card from Topps' 1978 Star Wars set. Card #207 (fourth series) allegedly shows the famous golden droid sporting a penis that would put John Holmes to shame.
What we appear to have here is an image created by the combination of a natural part of our robot friend's nether regions (the area inside the red rectangle below) and something extra (the area inside the green rectangle below) added through methods unknown. The result is a decidedly well-endowed droid:
Just how did this image end up on a trading card? As usual, legend places the blame on a disgruntled artist, just as in the examples of the infamous cover from Disney's The Little Mermaid video and the notorious Renuzit air freshener can. But according to the official Star Wars web site, what's seen here is just a "trick of timing and light":
[I]t appears that the extra appendage is not the work of an artist, but rather a trick of timing and light. The untouched archive photo shows the image just as it appears on the card. The current theory is that at the exact instant the photo was snapped, a piece fell off the Threepio costume, and just happened to line up in such a way as to suggest a bawdy image. The original contact sheets from the photo-shoot attests to this. They are not retouched in any way, yet still contain the same image. Whatever the real explanation is, the 'mischievous airbrush artist' scenario simply doesn't fit.
Intentional or not, the depiction of a well-hung C-3PO was realistic enough that Topps later replaced the card with an air-brushed one featuring a tamer rendering, creating a new version that turned out to be scarcer than the original.