Being that it is hosted on another site, I can't control that photo so, unless it already had a thumbnail there is no way to do it.
A member that has attachment rights (Contributor) such as yourself can copy the photo onto your own computer, then upload it as an attachement (50KB limit) and the system would create it's own thumbnail for it, like I did above.
Another way would be upload it to your gallery in a Misc. Album (Keeps it out of the general photo list) and then do the regular UBB code or use the Gallery Pop Up.
The code to make a clickable thumbnail, which gets done automatically when using the Pop UP, looks like this: (without the *)
[*url=http://vehicross.info/gallery/data/561/4moncha_top_of_world_eiji.jpg][*img]http://vehicross.info/gallery/data/561/4moncha_top_of_world_eiji-thumb.jpg[/img*][/url*]
The [img] of the thumbnail just gets nested in the [url] of the larger image.