Thanks for your reply, @[deleted], and for the link.
My issue is that my context menus are cluttered, and I would like to get rid of these three items. They are not installed, but that doesn't help. In fact it's worse, because if they were installed then I could uninstall them and their context menu entries.
I have both ShellExView and ShellMenuView. They do display pages and pages of entries from NCH, but they are all from WavePad. I had disabled them all in ShellMenuView, but that didn't do anything about the clutter entries.
I went into regedit, and found the three pieces of clutter under .bmp. I assume that NCH created entries under every other image file format (there are over 100 for WavePad), so I did not think it a good use of time to try to remove them all in regedit.
So I uninstalled WavePad. Fortunately that removed the context menu clutter as well. Unfortunately there are still a load of registry keys in Computer\HKEY_USERS\S-1-5-21-567311920-4282180155-3890509808-1000\SOFTWARE\Classes\ with pixillion - and presumably with photopad and photostage as well. I hope they won't cause problems. I wonder if NCH can tell me how to remove them.
I would love to reinstall WavePad, so would appreciate any other suggestions as to how to get rid of these context menu entries.