How to deal with mental issues because of someone's misbehavior?

These days these types of issues are happening. So it is always better not to post photos on social media accounts. Some people try to create problems for others by morphing the photos. Always prevention is better than cure.
Don't think too much about the issue. Hope he will not create any problems for you. If you think too much about the same issue unnecessary tension to you. Divert your mind on some other issue. Whenever you are getting some thoughts about the issue, start thinking something different. Otherwise, start reading some interesting books that you like. A fiction story or something similar to that. That will make you forget about that issue. Another way is to take up some puzzle solving. Sudoku or other mathematical puzzle-solving is the best way to divert your mind from the issue you are thinking,
Meditation and yoga are also useful in diverting the mind from unnecessary thought. Another easy way is to recite or chant some poems or slokas so that your mind will get diverted.
What are the tasks you have to carry out? Start thinking about those works and think about various ways of doing that act and start analysing the pros and cons of each method and evaluate. Once you start that automatically your mind will forget other issues.
Start writing somethings imaginary. Then your mind will go brisk on that imaginary issue and make you forget the issue of your photograph.
You can practice some of the technics described above and then you can see the results. Never try to use medicines for this, Once you start medication you may have to use them for a long time.

People are taking advantage of the pictures and information in the social media and sometimes are trying to misuse them by misinterpreting them or presenting them in a distorted form or modified form. We have to find out whether that boy is doing it habitually as he might also be doing these things with other people or he is doing it due to some grudge against you or some jealousy as you are doing a good work as the representative of the class students. Whatever be the reason it is not in a good taste and as you have not done anything wrong why you should be afraid or apprehended by the actions of that student. Please note that distorting or modifying facts in the social media is a criminal act and if the same is proved against him he can be booked for his offence by the cyber police. So one thing that can be done in this matter is that somehow this message should reach him either through some other student or even through messaging directly him in a stern way.
Some people are very soft hearted and sensitive and they are affected by these types of incidents and lose the peace of mind. But remember the world is full of such notorious and mischievous people and we should most of the time ignore them but if they go beyond limit then it is the duty of every citizen to complain about it and once they find that the other person is not as gullible as they thought then they would keep a low profile and change their ways. So, there is nothing to be perturbed and one must increase one's tolerance power as well as control on one's mind to tread ahead in this world boldly and face these small hindrances and obstructions in the usual way of life.
During the journey of our lives we meet any such obstacles and incidents which perturb us but keeping a cool mind and analysing those things and taking a prudent reaction and response to them is the essence of our judgement and knowledge. So do not feel let down by these fake charges made by other person with whom you do not have any friendship or relationship of any kind. Do your work with sincerity and seriousness and these small things would die with time and would be out of your memory.

The situation with which you are currently facing is worrisome for you but remember everything thing has its own limits. There are two ways of handling this situation the first one being the ignorance where you should not mind whatever he is doing and at the same time you should not be perturbed to the extent that your overthinking would ruin your studies and your other passion. He would try his level best to attract your attention and your cold responses would certainly discourage him to go ahead further and ultimately the current development will die down. But this needs a lot of patience from your side by not moving emotionally from his calculated mischiefs.
The second attempt would be to have a talk with the derailed boy and apprise him of your extreme step of lodging a complaint against him to the cyber police authorities. Here also there are twin possibilities- either he would refrain himself from such gimmick plays and finally he would come to terms. The other possibility would be that he would be aggressive enough to take revenge from you. Such a development would be suicidal on your part because in course of solving the issue, you might be entrapped to a situation where the possibility of amicable solution would be practically impossible thereby affecting your career.
Hence the best step in this connection would be the ignorance of such a nasty situation and believe me he would not go further if no response is forthcoming from your end.
Remain in the calm mind and concentrate on your ongoing studies so as to have a better future.