With C1ImageViewer, you can link to any image URL and display the image with an interactive magnifying glass. Both png and jpg files can be used.
The ImageViewer grabs the image using the URL provided and displays it in the Web Part. For a list of images with Creative Commons licensing, see http://www.flickr.com/groups/creative_commons-_free_pictures/pool/
You can move the magnifier around the image to zoom in on specific areas. You can also use the +/- keys.