Hello Linh and thanks for this essay.

As I noted already in another essay, you have too many introductory phrases.

To begin with, the use of television surveillance in public place might invade privacy rights of individuals. That is to say, when people recognize they are being monitored, they are likely to feel uncomfortable to act as normal to avoid making mistakes. To make matter worse, if information system is hacked by hacker, many sensational data could be leaked and spread out on the internet, which may damage severely these people’s lives, especially for celebrities who have always tried to keep their image.

However, CCTV contributes considerably to ensure public safety. To be specific, with application of CCTV in street corner and traffic lights, polices, in all probability, observe from a distance people who violate traffic rules such as jump the light, hit-and-run, which enable them to identify perpetrator. Even better, it is thanks to these qualitative evidences that make it easier to legal system prosecute criminals. Moreover, installation of CCTV promotes law-abidingness. In fact, the signs people see in shopping streets and buildings let them be aware that they are being watched by law enforcements. This, therefore, makes people far from dare to commit shoplifting and vandalism.

You have used them correctly, but there are just too many of them. Use one, or maybe two, per paragraph – no more! Think of them as salt: a little lends flavor, too much spoils the dish.

Three words to avoid: 'former,' 'latter,' and 'respectively' 

 Your writing should move forward. Never force the reader to go back to work out which one is 'former' and which one is 'latter', or 'respective', or 'respectively.'  Instead, mention the actual subjects again, showing the examiner some new vocabulary.

While it is maintained that installation of CCTV in public places is an effective measure to tackle the worsening situation, this belief is dismissed as violating the right to privacy. Despite the merits of the latter, the former is more persuasive.

It's a long construction, with many nouns, passives and phrases. It might be easier for readers if it was written like this: 

While CCTV in public places can deprive us of privacy, it can also reduce crime. In this essay, I will explain why I feel the loss of some privacy is a small price to pay for safer cities.

 

Don't worry about using "I feel" or "I believe." It's an opinion essay task. Task 1 in IELTS gives you a chance to use passives and show detachment, allowing the data to speak for itself. Task 2 is all about opinion. Use some passive if you like, but present your opinion.

Hello Linh

It's absolutely OK to use personal examples in Task 2 in IELTS (NOT in Task 1, of course).

Task 2 in IELTS writing asks you to give an opinion in an academic, "semi-formal or neutral" style, using language accurately. Of course, you shouldn't write "I wanna", "I'm gonna", use bullet points, or use words and phrases like "kids", or "He was, like, totally awesome."  (See https://www.teachers.cambridgeesol.org/ts/exams/academicenglish/ielts/academicwriting)

But you can and should give examples from your personal experience if they are relevant, and you should definitely give YOUR opinion. Don't hide behind words and passive phrases such as  

• It has been observed
• It is often claimed that
• It has been noted that

These are fine if all your writing is extremely good, but it's better for most candidates to write simply and just say what they mean.