If you have a SLR camera, it’s probably way over 10 megapixels. Some of the really fancy SLR cameras are more than 20 megapixels! One picture can be a massive size, 10 to 20 megabytes. If you want to share a really high-resolution picture with friends, you can’t unless you upload it somewhere and they download it to their PC.
Seadragon is a cool service from Microsoft that lets you upload really large pictures and lets you view it using their picture viewer. It’s way cool because you can make it full screen and zoom in and out by clicking.