Hi Pilgrim

Sorry my response took so long, I have been studying the issue a little more.

I am just going to give a fairly short answer at this time as I really don’t want to spend too much time on the issue. Saying that, I do not want to leave the impression that I think the matter is unimportant, because it is.

Do I believe that wearing a t-shirt with a picture depicting Jesus on it is breaking the second commandment?

Yes I do.

Do I believe that someone who wears such a t-shirt is living an un-Godly life and perhaps is not a true Christian at all?

Maybe, maybe not.

We all sin and sometimes it is done out of ignorance, rather than a deliberate intent to sin.
What is certain is such a person needs to be taught from Scripture the will of God regarding the matter and how to obey Him and apply it.
I also believe that although we should not water down the truth, we should be careful in our approach with the person. Being careful not to insinuate that we are calling into question their sincerity in why they would wear such a t-shirt.
I have been successful at this in the past by asking the person to exegete a particular applicable passage of Scripture. In that way, I am not so inclined to become overly judgmental in my attitude.
As things progress, depending on the person’s response a judgment can be made on how to proceed further.