I apologize if this has been asked before, but a search didn't turn up anything on the forum.

Is there a reasonably practical way to add additional canvas images to the built in gallery, so that users have a larger selection of available canvas images to choose from if they choose to select a new canvas image from the gallery rather than uploading one?

I'm not talking about changing the default canvas - I've already learned how to do that - but rather adding additional canvas images to the existing gallery. I've tried copying new canvas (along with matching thumbnail) images to the obvious locations where canvas images already exist, but I haven't been able to have the new images display in the selection gallery.

If adding new images to those available in the canvas gallery is possible, any information on how to do so would be greatly appreciated.