Robin Good: Zoom.it a free service from Microsoft allows you to create an infinitely zoomable image by simply providing a link to a high resolution image already posted on the web.
Once you provide the link Zoom.it takes over and gives you back both a link you can share anywhere as well as an embed code which allows you to post the "zoomable" version of your selected image inside your web site or blog.
"Zoom.it converts your image to the Deep Zoom format, which lets you smoothly and efficiently explore the whole image, no matter how large. Check out Deep Zoom Studio for examples of this technology in action."
You can also submit web site pages or PDFs. Image file formats supported include JPEG, PNG, SVG and TIFF.
The service is free to use and requires no registration.
More info: http://zoom.it/pages/faq/
Try it out now: http://zoom.it/