Consegui desabilitar todos os arranques de imagens (arrastar e soltar ainda funciona se eu realmente quiser uma imagem lá) sobrescrevendo uma função declarada no mac-win.el (arquivo não compilado não incluído na instalação padrão.)
no meu .emacs:
;; prohibit pasting of TIFFs
(defun x-selection-value (type)
(let ((data-types '(public.file-url
public.utf16-plain-text
com.apple.traditional-mac-plain-text))
text)
(while (and (null text) data-types)
(setq text (condition-case nil
(x-get-selection type (car data-types))
(error nil)))
(setq data-types (cdr data-types)))
(if text
(remove-text-properties 0 (length text) '(foreign-selection nil) text))
text))
original foi:
(defun x-selection-value (type)
(let ((data-types '(public.utf16-plain-text
com.apple.traditional-mac-plain-text
public.file-url))
text tiff-image)
(while (and (null text) data-types)
(setq text (condition-case nil
(x-get-selection type (car data-types))
(error nil)))
(setq data-types (cdr data-types)))
(if text
(remove-text-properties 0 (length text) '(foreign-selection nil) text))
(setq tiff-image (condition-case nil
(x-get-selection type 'public.tiff)
(error nil)))
(when tiff-image
(remove-text-properties 0 (length tiff-image)
'(foreign-selection nil) tiff-image)
(setq text (mac-TIFF-to-string tiff-image text)))
text))