HTML5 Offline Application: How to view TIFF files from localStorage (FileSystem API)

I have a potential customer who wants an application that can download large amounts of TIFF files locally on a machine for display.

After having discarded Java apps and Windows apps as too difficult to distribute (he has no control over the client computers) I am suggesting an offline HTML5 application.

TIFF is only natively displayed by Safari, and the FileSystem API only works on Google. WebSQL will be too small for the amount of data required (3-4 GB).

I've looked at different plug-ins (AlternaTIFF and BlackIce) but both need to be installed separately, which most of the users will probably find difficult to do.

I am wondering if there was a local TIFF Viewer that I could call from the browser that would open the TIFF from the FileSystem?

If this does not work, the last solution would be a conversion of the TIFFs to something else on the server, but it's going to make my database double in volume.

Any suggestions would be welcome!

UPDATE:

The target computers are not under the control of the client. There is no easy way to distribute the software to all the target computers. I'm assuming they are all windows machines, but it's no guarantee that .NET is installed.

That's the reason I opted for HTML5. At the moment I'm considering a Java Application launched with Java Web Application.

Customer has not yet confirmed the type of files they are using.

The customer is in the construction industry, the TIFFs are scans of large plans which (I assume) will need to be high-quality (zoomable, printable etc) so I don't think a rescaling to JPG will be accepted.

SECOND UPDATE

I'm coming to the conclusion that an HTML5 App is not going to be able to answer all the requirements. In particular there is one requirement that requires a multi-document print (select n documents and have them printed out in a batch). I'm starting to consider standalone applications that can be deployed and updated easily over a wide range of Windows configurations. I'm thinking of a Java Rich Client distribution over Java Web Start or a Microsoft application distributed via one-click-run. I'd simply write the files on the local filesystem and have the client display the images in-line. Would that be a good idea?