How about:
"Different tools, same man"
possibly followed by:
"[Inanimate] Objects can't commit murder."
Not sure whether "inanimate" makes it too long... also, the "commit murder" part might be turned around by the opposition and made to imply that gun owners are murderers (or some such nonsense), so I'm not sure whether its overall effect on the caption is positive.
I think the point to get across is that the observer is in no danger in any of the three pictures, but that kind of approach is easy to attack with the "get rid of the weapon, and he couldn't have killed" kind of counterargument. That argument makes a picture such as the one described difficult to use to promote firearm use/ownership, as it immediately elicits a strong emotional response from the opposition.
I liked bensdad's and Tallpine's approaches--showing a regular person with different tools, which could be misused, despite not being firearms, and showing the same person with a firearm, and making the point that the observer is in the same danger (or lack thereof) in each picture. Essentially, remove the opportunity for the opposition to say, "Get rid of weapons, you'll be safer," by subtly making the additional point that almost any hand tool (or bare hands) can be used as a deadly weapon, if the user is determined to do harm.
Anyway, those are my thoughts on the matter, for what they're worth.
