This is an issue that is of widespread concern nowadays, as the result of the spread of sin and all kinds of haraam things. There is hardly any field in which the shaytaan does not try to spread evil in it, so such an extent that the Muslims are become very confused about what is halaal and what is haraam, and it has become very difficult for them to purify their earnings and avoid any haraam elements in them. Allaah is watching the pious and He is sufficient for His believing slaves. He sees that they want to obey Him and hate to disobey Him, and He will reward them and grant them forgiveness.  

In Islamic sharee’ah, one of the principles of permissible business and trade is that it should not be something by means of which Allaah is disobeyed, so it should not be a means of sinning or lead to falling into haraam. When Islam forbids a thing, it also forbids everything that may lead to it or help with it, and Islam enjoins blocking all the means that lead to it.

Allaah says (interpretation of the meaning): 

“Help you one another in Al‑Birr and At‑Taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression. And fear Allaah. Verily, Allaah is Severe in punishment”

[al-Maa’idah 5:2]

Shaykh ‘Abd al-Rahmaan al-Sa’di (may Allaah have mercy on him) said: 

One is required to refrain from every sin and act of wrongdoing, and to help others to refrain also. End quote. 

Tafseer al-Sa’di (p. 218) 

It says in al-Mawsoo’ah al-Fiqhiyyah (3/140): 

According to the majority of fuqaha’ it is not acceptable to sell grapes to one who will use them to make wine, or to sell means of gambling to a gambler, or a house that will be used as a church, or to sell wood to one who will make it into a cross, or to sell copper to one who will make it into a bell. The same applies to everything which it is known that the purchaser intends to use it for something that is not permissible. End quote. 

If the seller, designer or producer is certain that what he designs will be used for haraam purposes, it is not permissible for him to sell it or produce it. The same ruling applies if he thinks that is most likely, even if he is not certain. 

But if he is in doubt, or he does not know how the item he is selling or producing will be used, then there is no harm in selling it and designing it, and the sin will fall on the one who uses it for haraam purposes.  

Ibn Hazm (may Allaah have mercy on him) said: 

It is not permissible to sell anything to one who will certainly use it to disobey Allaah, and such transactions are permanently null and void, such as selling anything that may be squeezed or pressed to one who it is certain will use it to make khamr (alcohol), or selling a slave to one who it is certain will mistreat his slave, or selling weapons or horses to those who it is certain will use them to attack the Muslims, or selling silk to one who it is certain will wear it, and so on, because Allaah says (interpretation of the meaning): 

“Help you one another in Al‑Birr and At‑Taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression. And fear Allaah. Verily, Allaah is Severe in punishment”

[al-Maa’idah 5:2]

The kinds of transactions that we have mentioned are obviously kinds of cooperating in sin and transgression, without going into detail, so annulling them is cooperating in righteousness and piety. 

If no such thing is known for certain, then the transaction is valid, because it is not helping in sin. If the purchaser disobeys Allaah after that, then the sin is on the purchaser only and not on the seller. End quote. 

Al-Muhalla (7/522). 

The same ruling applies to the brother who asked the question: 

If someone comes to you and you know that he wants to design a website that he will use for haraam purposes, such as riba-based banking or indecent pictures or selling haraam things such as alcohol, pork or cigarettes, or websites for movies and music, then it is not permissible for you to design the website for him, and it is not permissible for you to help him in the evil that he wants to do; rather what you must do is advise him and guide him and remind him to fear Allaah, may He be glorified and exalted. 

But if you do not know anything about the reason he is asking for website design, or if the site will most likely be used for permissible and beneficial things, then there is nothing wrong with you designing it and selling it, even if the owner will include some haraam things in it, because the rulings of sharee’ah are based on what is most likely to be the case and not on rare instances. 

See the answer to questions no. 22756, 95029 and 98062. 

With regard to the ruling on including pictures of children on the websites that you design, that is not permissible. We have stated previously that it is haraam to make images, whether they are drawn by hand or made with a machine (a camera), and no exceptions are made from this ruling except that which is absolutely necessary, such as pictures in passports and other things that are needed. See the answer to question no. 20325. 

And Allaah knows best.