I don't know how to help you purge the images, except perhaps to get some pleasant (or at least neutral) onea to replace it and consciously call them to mind when the intrusive ones try to take over?

All I can say is that I avoid images of horror in favor of text for that and other reasons, and hope you may choose to do the same going forward. Doing so is no betrayal to your conscience, but rather a preservation of your ability to act. Good luck.