kuujinbo, thanks, but that does not help, because it is a set of instructions for uploading files from one's computer (I run a forum that uses the same interface).
The image tag on this forum (the mountain icon above) is meant to do what I wanted; explicitly, to pull the image off DropBox by inserting its unique URL. If I upload any image files to my own server, the getDPI image tag works as intended. From a technical point of view, I can't see why the same tag can't pull a DB file into this forum. I will ask Jack to advise. Cheers and thanks, KL