Nothing except colors and shapes of things would be visible to eyes. Ears are not able to hear anything other than sounds. Material things 1- To complain:
One who was subjected to cruel treatment and torture may go to the ruler or social leaders requesting to extricate him from the torturer. In such a case, he may need to explain about that cruel person and the way that he badly behaved towards him. Though it is a talking about a person's cruel behavior and he will surely does not like it, it is religiously allowed in Islam. There is no need to worry about whether he likes or not. It's very clear that Islam, as a religion, never protests against self-defense or dealing with the way to keep self respect, but always goes all-out to wipe out troubles and violence from the earth. The holy Quran Says:
“Allah does not like that the evil (matters) should be uttered in public except by him who has been wronged (tortured)" (Surat AnNisa: 148).

2- When a person indulges in immoral and irreligious activities, it is quite common that we urge to get him in the right path. According to Islam, in such a condition it is allowed to ask some one, who has some authority over that person, to influence him to hold him back from doing bad things. It doesn't matter whether he does or doesn't like talking about his bad doings to another person. “When a person, called 'Aboojandar', was drinking alcohol in Syria, another person discussed the matter with Caliph Umar Bin Khathaab(R), and then Caliph Umar(R) made a diligent effort to restrain him from drinking. But, Caliph Umar (R) neither hated the person who came to discuss the matter nor scolded him for backbiting". (Ihya Uloomudheen: Vol 3, page 152)

It is heartrending to see many people who always immerse in worst doings like prostitution, gambling, drinking, and cheating. As to maintain a better social life, we all need to do the best to hold them back from this sort of blasphemous activities. Therefore, discussing the matters with those, who can influence the evil doers, in order to show them the right path, even if they don't like this talking, is far better than keeping silent for the sake of selfishness and being involved in the sins.

3- To seek fathwa (to seek Islamic law from scholars):
When we seek fatwa regarding a matter, it is not forbidden in Islam to talk backbiting about some one in relation with the matter, if it needs so. For instance, explaining the cases like 'my father tortured me', 'my husband behaved in such a bad manner', or 'my brother attacked me in such a way' in regard to fatwa seeking is some thing necessary to get correct answer from mufti (Muslim scholar who is able to find out and give fatwa). Though it is backbiting because father, husband and brother almost certainly don't like this kind of talking, it is allowed in Islam so as to facilitate fatwa seeking. Explaining the cases in its reality by giving the true pictures would be more helpful to the mufti to find out and give appropriate laws than just mentioning by some ambiguous words like 'one father' or ' one husband' or 'one brother'.

A Mufthi should be well advised in taking the decision. He should think deeply about all the factors related to the cases. He must analyze and scrutinize all the parties and situations as well which relate to the cases before he comes to a decision. For instance, there occurs an incident in a place and two people seek fatwa regarding with the same. If both get different answers from a mufti it may cause arguments between two groups of people and fighting among them. If mufti had taken the decision carefully after analyzing the problems effectively, the arguments and misunderstanding that happened many time among the public could have avoided.

The following Hadîth teaches that all the circumstances of and all the parties to the cases must be very clear to the mufti.
“Zainab (R), wife of Abdullah ibnu Mas'ud, and one lady from among 'Ansar' people, once went to Prophet Muhammad (s) to seek fatwa regarding a matter. But they couldn't ask (directly). They requested Hazrat Bilal (R) to seek fatwa from Prophet (S) on behalf of them and to get the proper answers for their cases. They reminded him not to inform who are they. He went to prophet(S) and explained their cases. Then Prophet of Allah asked: 'Who is asking the question'. Bilal (R) told that Zainab and one lady from Answar people are asking the question. Upon this the Messenger of Allah (S) said: Which of the Zainabs?(many are there in the name of Zainab) Then, Bilal (R) made it clear to Prophet Muhammad(S) that it is the wife of Abdullah Bin mas-ood" (Muslim).

Narrated Aysha (R): Hind Binth Uthba(R) once asked Prophet Muhammad (S): O Allah's Apostle! My husband Abu Sufyan is a miser, so is it sinful of me to feed our children from his property?" Allah's Apostle said, "No, except if you take for your needs what is just and reasonable" (Bukhari and Muslim). Even though Hind (R) tells that her husband is a miser, and he probably will not like it, it is not regarded to be backbiting in Islam.

4- Islam teaches that a Muslim must make an effort to reduce the bad behaviors of the people like fraudsters, rogue and selfish. But it is not considered to be backbiting in Islam to publicize the vulgar behavior of these kinds of people so as to get the public protected from their disturbances.

'When a person asked the permission to come in and meet prophet Muhammad (S), he told his companion to allow him to come in. Before he came in, Prophet of Allah had already explained to his companion that he is the worst one in his family' (Bukhari and Muslim) Prophet Muhammad (S) had introduced that person to his companion in a way that he may not like it, that was only to make the companions careful when dealing with him. Similarly, it is mandatory for a Muslim, who knows his friend better, to reveal his bad characters and defects as well to those who are going to handle marriage or business with him.

When we see, or realize that some one deceives the customers by giving incorrect weight and selling poor quality or defective goods without informing them, we are responsible to disclose the fact to the customers. Fatima binth Qais reported: My husband Abu 'Amr b. Hafs divorced me absolutely when he was away from home, and he sent his agent to me with some barley. When my period of 'Idda' was over, I mentioned to him that Mu'awiya son of Abu Sufyan and Jahm had sent proposal of marriage to me, whereupon Allah's Messenger (PBH) said: As for Abu Jahm, he does not put down stick from his shoulder (he always hits his wife), and as for Mu'awiya, he is a poor man having no property; marry Usama b. Zaid. I objected to him, but he again said: Marry Usama; so I married him. Allah blessed there in. (Muslim)

5- When someone does irreligious activities and he feels proud of it, it is not regarded to be backbiting in Islam to talk about it.

6- When someone is famous in the name of blind or lame, it is not sinful to address him like that to the public to make them understand easily. But, we should not do so, if they hate it. All the abovementioned circumstances of backbiting would be allowable in Islam only if we do not mean hurting or insulting the friend by our talking.