Gigapixel images are large-format digital photographs that contain several orders of magnitude more digital data than photographs taken with your typical DSLR. Instead of several megapixels in an images, we're talking tens of even hundreds of gigapiexels. No single consumer digital camera takes photos in the gigapixel range, so they're created by stitching together photographs taken with automated rigs (as we explained in this post from a while back). Organizations such as the Gigapxl Project aim to archive photographs of American buildings and monuments of cultural significance, including State Capitols and National Parks. One of my favorites is of the Space Shuttle Discovery at dusk. But even these awesome images are dwarfed by the very largest of gigapixel photos, as cataloged on Wikipedia, with most of these massive photos taken of dense cityscapes. The current claim to the largest digital photo is Shanghai-272, which was released as an interactive zoomable photo online in late 2010. You can pan and zoom around the 887276x306908 pixel image in real-time, spotting close-up details even in skyscrapers miles away--this takes the idea of "enhance" to a whole new level. The photo was created by over 12,000 individual images taken with a Canon 7D and a 400mm f/5.6 lens over eight hours. And according to the photographer, gigapixel photography is a highly competitive field, so it's only a matter of time before the next largest image is created.
This reddit thread brings renewed interest in the 2010 photo, as commenters play a Where's Waldo-like game of identifying unique individual objects in the Shanghai-272 photo. My favorite found object: a street sign apparently banning trumpeting.