Assalamualaikum warahmatullahi wabarakatuh.
Bismillahir rahmaanir rahim.
It has been mentioned in a hadith of Nabi SAW that:
'Whomsoever sees from amongst you a disobedience being done, therefore he should avert it with his hand. If he is not capable of doing so, then with his tongue. If he is not capable of doing so, then with his heart and that is the lowest form of iman (faith).' (Muslim)
Taking pictures of animate things is strictly prohibited in Syari'ah due to various ahadith (pl. of hadith) and proofs which can be found regarding this issue. Alhamdulillah, you dislike it when anyone tries to take a picture of you as you have, by realizing it or not, practised on the hadith mentioned above since taking pictures is without a doubt, an act of disobedience towards Allah.
Like how the hadith has stated, we should try to our utmost best to avert the disobedience either by action, speech or intention. However, when all of these means fail to avert the disobedience, we shall not be held responsible on the act of disobedience committed because we have tried our best to prevent it.
An example which can be easily understood is like when our mother tells us not to be on the internet for too long as the solah time is about to end and we ignore her. When we look at the time and want to pray, we've realized that the solah time has already become qadha'. So whose fault will it be then? Our mother's or ours?
Similarly in your situation, you have tried to prevent people from taking pictures of you but they still do not take heed of your requests, therefore you will not be accountable for their misdoings.
Maybe you can try telling them that different people have different likes and dislikes; some people dislike rude people, others cannot stand just being at home doing nothing, some like cooking, others dislike reading books, etc. and you dislike it when people take pictures of you.
When someone does take a picture of you in future, do not just leave the matter as it is, but rather try to make a firm statement saying that you do not like it when people take pictures of you and insist that person to delete your picture immediately because that has made you upset. On seeing your firmness, they will then learn and know not to repeat the same thing again insya Allah.
Please click on this link for some beneficial material you may use to reason why you do not wish your pictures to be taken in future:
http://www.muftisays.com/qa.php?viewpage=viewQA&highlight=%20picture&question=1047And Allah knows best.
Wassalam.
