Syria crisis: Counting the victims
Exactly how many people have been killed during the repression of the uprising against the rule of Syria's President Bashar al-Assad?
The movement of foreign media and independent human rights organisations has been severely curtailed within the country, making the verification of casualty figures almost impossible.
Recently, the presence of UN monitors has provided another source of information - as with the massacre in the village of Taldou near Houla - but for the most part, the outside world has been reliant on casualty figures supplied by opposition activists.
Syrian government sources and the state-run Syrian Arab News Agency Agency (Sana) have been issuing casualty figures for specific events, but official estimates of the overall death toll have been more sporadic.
In early April, Sana quoted a letter from the Syrian foreign ministry as saying 6,143 Syrians, including both soldiers and civilians, had died since the beginning of the crisis, placing the blame on "armed terrorist groups".
In the same letter, the foreign ministry sharply criticised UN High Commissioner for Human Rights Navi Pillay for what it called "bias" in her comments on Syria.
The Office of the High Commissioner for Human Rights (OHCHR) in Geneva had been providing some of the most widely quoted estimates of death toll earlier in the uprising.
However, in December, the OHCHR stopped trying to produce estimates because verifying the toll had become too difficult.
Up to that point, the OHCHR had been taking figures from "five different organisations who were compiling lists, and then coming up with our own... figures, tending towards the cautious end of the spectrum," according to Rupert Colville, spokesman for the OHCHR.
It is an approach that is also used by some activists; sharing information in an effort to better corroborate it.
Two of the organisations that the OHCHR had used were the Syrian Observatory for Human Rights (SOHR) and the Violations Documentation Center (VDC). Those behind these sites say they run verification on reports of casualties.
After initial reports from activists and volunteers in the field, those at VDC say they try to add "video clips, pictures of the martyrs, or any other details about the victim".
The data is periodically audited by sending it back to activists in the field for correction and addition of any missing information.
However, VDC does admit that these steps "do not present the possibility of a complete and full checking of the information".
Identifying the dead
Furthermore, the methodologies of the different sites vary and the tolls they have arrived at differ greatly.
For example, as of 29 May, the Syrian Observatory for Human Rights had put the number of civilian dead at 9,183, with 3,821 dead from the security forces.
However, at the same time the VDC had a tally of 11,884 civilians killed and 2,159 casualties from the military and security forces.
Another opposition website referred to by some branches of the UN, Syria Shuhada (Syria Martyrs), had an even higher number - 15,344, of which it says 14,072 were civilians, the rest being defectors from the military. It does not count deaths from regime forces.
The activists who run the Syria Shuhada website recognise that their estimates are consistently higher than those produced by other activists.
One reason they give for this is the wide range of sources that they gather their information from in the first instance.
Their figures are collated from other opposition websites and cross-checked, but they say that since becoming more well-known in Syria they have also received information directly from protesters' "committees".
The other reason for the higher figure is that they record deaths even when no name is given for the individual.
"Many of these have videos attached to them or are from sources we trust," the activists who run the website say.
"Other organisations don't accept bodies with no names which seems ludicrous to us," they add.
A UK-based activist who has been making his own efforts to compile casualty figures, Mahmoud Ali Hamad, says another issue is the large number of people who have been detained.
"If months have passed after someone being detained and they're not heard of again and we don't even know where they are - then they're considered dead," he says.
"Even before the start of the uprising, this is deep down in people's consciousness in Syria," he adds.
Even though many websites document victims' manner of death, or keep separate lists of the detained, he suggests that this may be causing some discrepancy in the figures produced by different groups, if some are including the numbers of missing in their death tolls.
Effects of violence
Those trying to stay in touch with activists in Syria say the upsurge in violence this year has complicated the issue further as many of those who were reporting deaths to the outside world have been killed or displaced themselves.
"Lots of my contacts in Homs have died, and many people have left," Mr Ali Hamad says. "It's a chaotic situation."
Activists in the US who set up the Syria Tracker website say that "with the escalation of violence starting in February 2012, some groups have needed to change their methodologies... and relax some of the controls they are placing" on recording deaths.
And what of the danger of exaggeration of the data to garner sympathy for the opposition?
"It's not fair to expect people in that situation to be unbiased," Mr Ali Hamad says. "This regime is their ultimate enemy."
"So even when I'm talking to people who I went to school with, I am taking into account that they are traumatised people. I don't take their word for everything."
He says there have been instances where has had to "weed out" sources because they have exaggerated, but says that this hasn't affected the integrity of his work.
Those at the Syria Shuhada website are even more vehement.
"There is absolutely no exaggeration of the data," they insist.
"Anyone who says this is the one driven by politicisation," they add.
They say they believe many victims' relatives are too frightened of retaliation to report casualties and that the true figure must therefore be even higher.
Mr Ali Hamad, while admitting he wouldn't use some of Syria Shuhada's methods, agrees that "the numbers reported in the first instance always turn out to be lower" than those which emerge after verification.
Whether and how to count casualties among army defectors and the Free Syrian Army (FSA) is another point of contention.
Even some websites that keep separate tallies for civilians and those involved in armed opposition class fallen FSA fighters as "martyrs".
Preserving a memory
Most of those involved in trying to collect the information admit that current conditions in Syria simply do not allow for an accurate toll.
"Everyone needs and wants a number - including us - but the cost for us of getting it wrong would be high and could undermine the credibility of our human rights reporting," Rupert Colville says.
So should the attempt to compile figures be abandoned?
"The UN and NGOs can stop trying, but we Syrians can't," Mr Ali Hamad says.
"I have lost cousins, schoolfriends in Syria. The only thing that keeps us going is that some day we will be able to hold accountable those who have killed people simply for expressing an opinion," he adds.
Those at Syria Tracker say: "In the long run, we don't feel that the specific counts are as important as the individual names, dates and places, which can be edited, updated, and revised over time.
"When the most accurate tally is collected and correlated across the different sources... we only hope that we can preserve the memory of a victim that may otherwise be forgotten."