I have only heard of these types of situations third-hand. Are there jurisdictions where it's actually ok to shoot someone because of where they're walking? I mean, is that really reason enough to shoot someone? Don't they need to at least threaten you or something? And is it actually ok to stop on the road and threaten (or hint) to shoot someone like that? There exist offenses like uttering death threats, and they're taken seriously. You can't just threaten to shoot people just cause you feel like scaring them, can you?
Based on the Texans that I know I don't think your chances of getting shot taking pictures are that great. On the other hand I wouldn't wear a serape If I was you. I don't know if you've read your newspaper lately or even if it's been covered by the press up north but the number of ranchers that have been shot or killed in southern Texas and the significant property damage by illegals or drug smugglers lately might make most get a little touchy.
Glad to hear it's an exaggerated concern. I like the cold, so I don't expect to be visiting anytime soon. If I ever ever up standing on a Texan's porch, I'll try not to look too menacing, lest they feel threatened, but I shoot Oly and Sony, what if he's a Canikon man?