I would like to configure it so that it only accepts one image drop, after that first image is dropped it is displayed in the image well and no other image drops must be accepted.
This thread from the NUG has some tips. According to this you cannot disable the ability to accept files after setting it so that you can. There may be changes to that functionality since this is a rather old thread, but it’s all I could find.
I might suggest you reconsider your idea though. I don’t know what your app needs, but often when I drop in the wrong image to something, I will drag the correct one in shortly after. Disabling the new drop wouldn’t allow your user to change the image should they make a mistake and drop the wrong one.
You can’t prevent a subsequent drop, however if you handle it yourself, you can replace the image with the image from the first drop. It’s a bit of a hack, but it’s possible.
As Tim recommends, this is not familiar functionality with other applications, which may confuse users.