Delete embedded image in Thunderbird e-mail message
If you have an image file attached to a Thunderbird e-mail message, it's easy to delete at the bottom of the message, by right-clicking and selecting Detach. But if the image is embedded, you don't have that option.
In order to detach an embedded image in a Thunderbird e-mail message you need to display it as plain text:
View > Message Body As > Original HTML
The embedded images are not listed:
View > Message Body As > Plain Text
The embedded images can now be detached: