This won't do all you want exactly like you want, but...
You could place a copy of the field on a dedicated layout where you can re-size the image to be much larger than your main layout. Then you can place a button that either takes the user to this layout or even pops it up in a new window.
Is it possible to create a button that will follow the path and open this image in Picasa for example?
I think so. I know it works for other apps (as long as they're installed on your machine, of course).
Simply store the images by reference and then double-click the field to open it.