Several times I have needed to delete a disk image that contains sensitive information (passwords, private keys, nuclear secrets , etc.), and I have always had to reboot with the image mounted so that I could wipe the contents before I deleted the image.

It would be much more convenient if there were an option in the "Edit Disk Image" page that allowed us to wipe an unmounted disk image. I'm not looking for any kind of secure erase algorithms, but a simple zeroing would keep the next linode that allocates the freed space from reading it.

This should be done automatically when a disk image is deleted.

Have you considered using something like EncFS?