In Italy, cigarette packs carry shocking pictures of diseased lungs, tumors, and other severe health effects, yet they fail to deter smokers. It’s essentially a cultural problem.
The existing ones, sure - you get used to it. But for non-smokers, that's a visible indicator of what you're bringing on yourself if you start smoking, so it has a deterring value. It helps you to present an abstract idea into something palpable that you can't ignore that easily.
Something has deterred smokers: the overall rate of adults who smoke has fallen from 50% to 25% in the last 50 years [0] - the source gives measures by gender and birth cohort, but you can aggregate them any way you want to see a big drop off.
I have been thinking why not take similar actions against alcohol as with tobacco. Add warning labels, increase taxes to huge number. Maybe ban anything but 94% pure stuff. No more any type of flavourings like they did with menthol.
The existing ones, sure - you get used to it. But for non-smokers, that's a visible indicator of what you're bringing on yourself if you start smoking, so it has a deterring value. It helps you to present an abstract idea into something palpable that you can't ignore that easily.