It's obviously a real picture of a real cemetary with real people buried in it.
The joke itself is fine, but use a hand-made graphic of a cemetary, not a real picture of a real cemetary with real loved ones buried in it. It isn't the joke that makes it tactless, it's the picture that was chosen.
If someone can't undestand how this can be tactless, then try to imagine the picture is instead of your loved one's actual tombstone (even if you can't read the markings, you still recognize it). How would that make you feel for your loved one's tombstone to be used as a gimic within a joke even if it wasn't meant to harm anyone?
No, I don't recognize a loved one's tombsone in the picture above, but I was simply thinking of others' feelings, including the fallen soldiers themselves.
I'm sorry if I have over-reacted because I have served and know those who have fallen while serving and thus have some sympathy and honor for them. Through my eyes I see something that should be held in a place of honor being used as a gimic in a joke. Call it over-reacting, I call it having respect, honor, sympathy, you know, human feelings.