ISIS allegedly beheads Croatian captive

 An image posted online appears to show that ISIS captive Tomislav Salopek of Croatia has been beheaded, the SITE Intelligence Group said Wednesday.

Salopek was kidnapped July 22 in the area of Cairo, according to his employer and the Croatian government.

CNN could not independently confirm the authenticity of the image, and Croatian and Egyptian officials have not confirmed Salopek's death.

In a video distributed online August 5, a group claiming to be ISIS' branch in the Sinai Peninsula threatened to kill Salopek if Egypt didn't release female Muslim prisoners in 48 hours.

Kneeling in a jumpsuit in front of a masked, knife-holding man in camouflage, the hostage identified himself as Salopek and read from a paper, saying he was captured July 22 and worked for a French geoscience firm.

Ardiseis Egypt, part of the French firm CGG, said the hostage in the video appears to be Salopek, who it says was a subcontracted worker who was kidnapped last month in Cairo.

The Croatian foreign ministry said last month that armed men stopped and kidnapped a Croatian national with the initials T.S. in Cairo while he was driving to work for a French-owned company. The ministry identified the captive in subsequent news releases as Salopek.

Releasing gruesome videos and photographs has become the hallmark of the terrorist group, one of the most brutal to emerge in living memory. ISIS has released photos of young men being shot as well as videos of beheadings, of a captive being burned alive and of prisoners in a cage being gradually submerged until they drowned.