At this time the JavaScript Diagram control cannot decode images from bytes saved in diagram files. It can only show images if they are specified via the ShapeNode.ImageUrl property. What you could do is set both ImageUrl and Image in the Windows Forms application, and distribute the images as separate files together with the diagram file.

Alternatively, after loading a file in MvcDiagram, loop over all nodes and call the node.Image.Save method to save the bitmaps in some image cache folder, and set node.ImageUrl to point to the corresponding file.

I hope that helps,
Stoyan