Origin of the 12 of 12
The 12 of 12 was introduced for January 2006 by Chad Darnell. He invited his weblog's readers to capture a dozen photos defining their daily routine with at least one body part in each of their photos. The goal was to have the submissions show how different people from all over the world live the same day. That first 12 of 12 drew sixteen entries (including Mr. Darnell's own). Mr. Darnell wrote in a recent e-mail "Since that time, we had Facebook and Twitter pop up, so now there are other projects that seem to have the same idea of sharing or updating people they are connected to, sharing their day, but it's now down to 140 characters a pop.  At least with pictures, they tell a story." He continues to host the listings of the 12 of 12 participants from all over the world who submit their project by posting their name, location, and permalink URL to the comments of his blog.

Enter the Geocachers
Sonny of the Podcacher Podcast introduced the 12 of 12 to the Geocaching Community in April of 2006 during their "Show 49.1: The Caching Commute." As more Geocachers created their own 12 of 12 entries a thread in the Podcacher Forums began taking submission for December 2006. Geocachers from many countries are submitting their photos from the twelfth day of each month to that same thread with or without Geocaching activities included.