On Sunday, shocking footage emerged from the Syrian city of Homs in which a man appears to be shot in the head by a sniper.

The video (which some viewers may find distressing) seems to show the cameraman being fired on by a sniper hiding in the shadows. The screen goes blank, then moaning can be heard, along with cries for help.

It is a chilling depiction of senseless violence against a (reportedly) unarmed civilian. Activists say Syrian forces are now targeting those seen filming on mobile phones.

This footage marks the latest in a series of horrifying images, videos and facts that have been trickling steadily out of Syria since Bashar Assad's regime began its crackdown in March this year. Other videos to have emerged recently include scenes of a teenager being wounded during protests in Hama, and graphic footage of the mutilated body of a 13-year-old boy (which again may be found distressing by some viewers). But because foreign journalists and human rights groups have been banned from the country, it is nearly impossible to authenticate the sources of such information.

A quick glance at the comments on the YouTube page of the sniper video is enough to see that scepticism and distrust is rife -- in Syria as much as in the wider international community.

One commentator dismisses the video as a fake, saying: "r u [sic] guys serious.. I can perform better even though I'm not an actor... I have seen a lot better fabricated films.. the quality is getting worse, running out of money may be..[sic]"

Events in Syria are demonstrably dangerous, and president Assad appears happy to do whatever it takes to cling on to power -- but it is telling of both the regime's propaganda machine and the wider problem of verifying information that such footage has not simply been taken at face value.

Although the videos may well be authentic, it is very difficult for anyone outside Syria to know that as yet. Online activists will not be quick to forget the lesson of Amina Arraf, the gay Syrian blogger who turned out to be an American graduate student living in Scotland.

A separate video, also posted at the weekend, seems to show the killing of activist and blogger, Diyya al Najjar, as security forces clash with protesters in the al-Qarabis neighbourhood of Homs.

For Assad, the evidence seems to be steadily mounting against him -- but we in the international community must also be wary of believing everything that we hear, and keep our eyes and ears open to the truth.