His battered and bloodstained body hung for three days on the cross on which he was crucified.

Around his neck, the Islamic State butchers who killed him had hung a handwritten placard accusing him of apostasy — abandoning his religion.

He was just 17 and the placard explained that the unnamed boy's crime had been to take photographs of the terrorist organisation's headquarters in the Syrian city of Raqqa, which has become the de facto IS capital.

Images of his body were smuggled to the West in defiance of the city's terrifying religious police by undercover activists appalled at the daily brutality taking place in their city.

Had they been caught, they too would have been killed; either crucified in Raqqa's central square like this poor teenager or beheaded before a mob.

Life in Raqqa once revolved around cotton farming. Muslims and Christians once lived together here and the sexes mixed freely. Now it is in the hands of the barbarous jihadi group, Islamic State

A group of captured Yazidi and Christian women are chained together and marched to a sickening sex slave market where they are sold to become wives for Islamic State fighters

Raqqa is the epicentre of global Islamic terror, a place where the barbarism of Islamic State is matched only by the sophistication of its ideologues in using social networking to recruit Muslims from across the world to their 'cause'.

This is the hellish city to which the three Dawood sisters, who vanished after telling their families they were on an Islamic pilgrimage to Saudi Arabia, are now said to be heading with their nine children, aged between 15 and three.

Meanwhile, their distraught husbands beg them to return home to Bradford.

Life in Raqqa once revolved around cotton farming. Muslims and Christians once lived together here and the sexes mixed freely.

Visitors could even sip a cold beer on the balcony of the Karnak Hotel and watch the colourful, bustling street scenes, western music blaring.

Displaced women and children from the minority Yazidi sect. In Raqqa, kidnapped women and any opponents of the ISIS regime are forced into sex slavery and expected to satisfy fighters returning from battles

Now, there is no longer music, dancing or joy. Men and women cannot mix any more. Gays are killed as heretics, hurled by IS thugs from a tower on the main square as people crowd the streets below. If the fall fails to kill them, as happened earlier this year to two men, they are stoned to death.

This is where Western captives with shaven heads and orange jumpsuits were held and tortured in tunnels by the likes of Jihadi John, real name Mohamed Emwazi, the murderous graduate of London's Westminster University.

Spanish journalist Javier Espinoza, seized in 2013, described how he was forced to the ground in his cell as Jihadi John pressed a long metal sword used for beheadings against his neck. 'Feel it? Cold, isn't it?' taunted the London-accented executioner. 'Can you imagine the pain you will feel when it cuts? Unimaginable pain; the first hit will sever your veins. The blood mixes with your saliva.

'The second blow opens your neck. You wouldn't be able to breathe through your nose at this stage, just your throat. You would make some amusing guttural sounds.

'I've seen it before; you all squirm like animals, like pigs. The third blow will take off your head. I'd put it on your back.'

Raqqa is the epicentre of global Islamic terror, a place where the barbarism of Islamic State is matched only by the sophistication of its ideologues in using social networking to recruit Muslims from across the world

Astonishingly, Espinoza was released by the extremists last year but seven of his fellow captives, including aid worker David Haines and charity worker Alan Hemmings, were beheaded.

Death stalks the streets of Raqqa, where smoking has been banned and a sneaky cigarette can cost you your life.

The shisha cafes where people relaxed have been closed at gunpoint. Passports must be surrendered.

Everyone has to attend, on pain of death, prayers five times a day. The only thing about which there are no restrictions in this dusty city is terror.

Those caught disobeying Raqqa's rulers face being dragged to the main square — where families once strolled eating ice creams in the evenings, their children cavorting on bikes amid squeals of laughter — to face brutal, summary punishment.

Spanish journalist Javier Espinoza, seized in 2013, described how he was forced to the ground in his cell as Jihadi John (pictured right) pressed a long metal sword used for beheadings against his neck

After Friday prayers each week, men, women and families are forced into the square as charges are read out against those accused of un-Islamic behaviour. Then the bloodbath begins.

The hands of thieves are hacked off with cleavers. Adulterers are beheaded with medieval scimitars. A street magician was beheaded after his tricks were branded an insult to Islam as they created 'illusion and falsehood'.

Severed heads are impaled on railings in the main square, once known as Paradise Square, and the bodies of unbelievers are left to rot on the streets, food for the city's stray dogs.

'It is like a waterfall of blood,' says Abu Ibrahim, a Raqqa resident and witness to the weekly punishments. 'There are more and more executions and now the children watch like they are used to it.'

Many of the atrocities have been documented by the terrorists and issued on the internet; used as a rallying call to Muslim supporters around the world, who are told that it is their duty under the Koran to come to live in this new Muslim State.

Khadiga Bibi Dawood (left) with her children Muhammad Haseeb (centre) and Maryam Siddiqui (right) are believed to be living in Raqqa. Khadiga Dawood, Sugrea Dawoood and Zohra Dawood are all thought to have travelled to Syria to join ISIS

The Dawood sisters, whose younger brother had already fled to Raqqa, heeded that call, despite the horrors in store for them and their children. Determined to brainwash the next generation, IS kidnap children in Raqqa's streets and take them to three Islamic 're-education' camps dotted round the city.

When they return, the children denounce their parents as apostates or non-believers, condemning them to arrest and torture. 'They are poisoning the minds of our children,' an underground Syrian activist told me on the telephone.

'They take them to a place called the Sharia Camp for Lion Cubs. They accuse their parents of being enemies of God if they are against the Islamic State.'

In the streets, boys as young as five play a game of executing infidels. One video smuggled out of Raqqa shows four children playing Western hostages, kneeling in a ditch, while another child recites the charges in Arabic before shooting them all in the head with a toy gun.

These children have also been pictured beside severed heads.

Raqqa is surrounded by mass graves, where thousands of Syrian government soldiers lie after being executed in the cotton fields.

Armed with Kalashnikovs, gangs of 'moral police' called the Hisbah (Accountable), patrol the city to check that women, who must be covered from head-to-toe in black Islamic garb, are either married or related to any man in their company.

Akhtar Iqbal, husband of Sugra Dawood speaks during a news conference to appeal for the return of his missing wife and children, in Bradford.

There is an all-female group of Islamic State fanatics, too, who patrol the streets to ensure there are no breaches of 'immorality'. Known as the al-Khansaa Brigade, they are as savage as the men and are also IS's most potent spying weapon.

Some of this feared brigade pose as housewives, mingling with the crowds, always listening for any sign of dissent.

Cynically, this brigade also runs brothels, where kidnapped Christian women, Yazidis from a nearby sect, and any opponents of the regime are forced into sexual slavery and expected to satisfy fighters returning from battles.

This is also the likely fate of foreign girls who have flocked to the city to become 'jihadi brides'. Girls such as Amire Abase, 15, Kadiza Sultana and Shamima Begum, both 16, the three East London girls who entered the city this spring after leaving their homes.

Like dozens of other young people from Britain, they were lured on social networking sites by promises of adventure and romance.

Raqqa today does not offer romance: instead, these highly prized foreign women are expected to have sex with dozens of jihadis.

To get round Islamic laws which forbid adultery, the women are married to jihadis and spend a week with their new 'spouses' before they are 'divorced' by a cleric and married to another fighter for another week.

Women who have escaped Raqqa, having gone there willingly in the belief they would marry and look after one fighter, have told how they were used as prostitutes. One woman said she was forced to sleep with up to 100 fighters.

When IS fighters took control of Raqqa last year, they demanded all unmarried girls be brought to their bases so they could perform their 'duty in jihad' and have sex with the fighters

The extremists insist that 'Jihad al-nikah', or sex for warriors involving extramarital relations with countless partners, is a legitimate form of holy war since it 'gives comfort to fighters'.

Indeed, when IS fighters took control of Raqqa last year, they demanded all unmarried girls be brought to their bases so they could perform their 'duty in jihad' and have sex with the fighters.

Posters appeared on city walls, reading in Arabic: 'We call upon the people of this county to bring their unmarried girls so they can fulfil their duty in sex jihad for their warrior brothers in the city and anyone who will not appear will feel the full force of the sharia [Islamic law] upon him.'

According to a sickening 'manifesto' issued to the people of Raqqa, a girl can be married at the age of nine.

It also reads: 'It is permissible to have intercourse with a female slave who has not reached puberty.'

Even some IS fighters have been appalled by this sexual sadism.

One, a 33-year-old called Hamza, who trained as an executioner in Raqqa, escaped recently to Turkey and told how he had been sickened by the rape of foreign girls brought to his compound.

'The commander tried to tempt us by saying that this is halal (lawful) for you, a gift from Allah that we are allowed to satisfy ourselves without even marrying them because they are pagans.'

Having risked his life to escape from Raqqa, Hamza branded his fellow fighters hypocrites. 'Some fighters were taking hallucinatory drugs; others were obsessed with sex. As for the raping, and the way different men marry by turn the same woman over a period of time, this is not humane.'

The horrific truth is being chronicled by a group called Raqqa Is Silently Being Slaughtered, its members constantly being hunted by extremists.

'It used to be a city like any other place, some parts were good and some bits bad,' one courageous dissident, called Abu Ibrahim, told me.

'We would go out and sit in cafes like any young people in another country. Then IS started abducting people and killing people in the streets. We did not know this would happen. We did not know that IS were here to kill us. Nobody talks, it is forbidden even to think.'