You may remove photos from your library and you may additionally delete them entirely from your hard disk.
This diagram shows how a photo, when deleted, is first put into Shotwell's trash. If you delete it from Shotwell's trash, it is put into your computer's trash. If you delete it from your computer's trash the photo is finally and irretrievably deleted from your computer.
Select the photos to remove and choose Edit ▸ Move to Trash. (You can also press the Delete key.) The photos will be moved from your library to Shotwell's Trash.
If you want to remove photos from Shotwell without having them pass through the trash, simply select the photos to be removed and choose Edit ▸ Remove From Library. The photo files will be left in place on disk.
Select the Trash entry in the Sidebar and Shotwell will display all photos that have been marked for removal or deletion. In the Trash view, the following commands are available:
Delete the selected photos from the trash folder.
Restore the selected photos into Shotwell.
Delete all photos from the trash folder.
When you delete files from the Trash folder or empty the Trash folder, you will be given the following choices:
Remove photos from the library but leave the photos in their location on the computer.
Remove photos from the library and delete them from the computer.