Can't delete a picture from the picture gallery because it is "in use"

I am trying to delete ("kill") a picture from the picture gallery, but it says the picture is "in use." I cannot see it in any window. I have used the Retrieve tool, but it says there are no offscreen objects. I cycled through the various windows and used "DrawAction delete," but that didn't help. It's just marginally possible that it's in some oddball layer, but I don't want to delete every layer because of the work it took to create them all.

What I want to do is delete the picture and replace it with a new version. But I can't replace it as long as it is "in use."

Igor thinks the picture is in use—why can't it tell me where? Is there some way to figure out where this picture is in use and delete it?

An issue like this has the potential to mess up an entire experiment for good: The only way around it would be to bring the picture in using a different name, then changing all the references in my code to refer to the new name. The old name and picture would then be some sort of dead baggage for the life of the experiment, which I would rather not have.

(A useful fix in Igor would be to allow replacement even if the picture is in use. After all, that's probably the main reason someone wants to replace a picture: to update it to a new version.)

I'm trying to think where a picture might be in use...

If it's in a graph or panel or layout, you should be able to find it in recreation macros.

It could be in a formatted notebook. If it's one of your broken pictures (as in your other thread) it might be hard to find.