There's an Android app called "Image Viewer" that'll view any gigantic JPEG by only decoding the part you're looking at. No special processing required, it'll take any JPEG off your memory card/you downloaded in the phone browser. I used it to view a high-resolution PDF bike route map converted to a 20 MB JPEG for viewing on the road - works great. The icon is ugly as sin though.
Figured that'd t be hard to find an image viewer called "Image Viewer" but it seemed almost impossible - even when restricting the search to ugly icons :p
Who's the developer/market-URL?