In reply to sbboy:
> Yes they are reported. As I mentioned already in my post.
> Like I said it means nothing to this person, twitter or instagram.
You're powerless to actually stop people infringing your copyright and as we've seen, the problem is more widespread than first thought, involving Flikr as well.
At least Flikr are prepared to take effective action. Less than 24 hours after my formal complaint, Yahoo has removed all my copied images from Ian Raistrick's Flikr albums. A modest result, but a satisfying one nevertheless.
It's a shame that Twitter and Instagram provide you with no redress or similar means of action.