Would it be possible to assemble an image on the browser by 'concatenating' other downloaded images together?

The use case is this.

The page will display 36 different tiles (small images). The user should be able to arrange those tiles into a 6 x 6 grid and save the resulting grid to disk as an image.

The best solution would be to do it all in the browser without Flash. The next best solution would be to allow the user to create the grid in the browser with simple JavaScript drag and drop functionality and then send the coordinates to the server for image processing.

The last solution would be to do it all in the browser with Flash. Is it even possible for Flash to create an image and then allow the user to save it from the browser?

I am familiar with the Pixastic JavaScript library ( http://www.pixastic.com/ ), but it relies on getting image data to and from a canvas element which is not very well supported.

What if I send the tile images to the browser as base64 encoded strings? Could I use JavaScript to create the 6 x 6 grid image? And if so, is there some way of allowing the user to get it onto disk without relying on the canvas element?