The standard IMG tag may not be the best approach when inserting really big photos because 1) wide images break the layout of your web page as they span outside the standard width and 2) large images are heavy in size so you web page loading time will become much higher.
If you were to insert such a big image in you web page, a very neat option is Zoomify which you can see in action below - your visitors can view (or even zoom, pan and scroll) the gigantic image in full resolution without leaving the current web page.
Update: Zoomify is no longer free but you embed large images using Google Maps tiles or with the help of zoom.it.
And since Zoomify renders the image in Flash, it's another good alternative for webmaster to prevent casual downloading of their images. Like Google Maps, the large image loads in tiles and only the visible portions are downloaded on the visitor's computer so the waiting time is reduced quite a bit.
You download a small executable from Zoomify website and pass on the image that would embed in the web page. Zoomify will slice it into tiles and you can upload the to any web space. Then you add a small Flash code to your web page that embed the Zoomify Flash image viewer. That's it. Everything is configurable including the initial zoom, menu bar, etc.
Zoomify is a commercial software but they provide a free version called Zoomify Express which is good enough for most of us - no restrictions, no image watermarks. Available for both Mac and Windows.