While deleting of images is possible from Ristretto each deletion needs to be confirmed through a dialog. Please add an option to disable this dialog and delete images directly.
Just had a look at the source code. For permanent deletion (Shift+Del) the dialog makes sense since it is basically an irreversable action. But there is no need to confirm moving files to the trash from which they can be restored anytime.
Dupe of 9989, which has a patch to implement an option for this. *** This bug has been marked as a duplicate of bug 9989 ***