Thanks for providing the image.
Let me start by saying I'm not a lawyer, nor am I trained in legal matters related to forums on the Internet. Questions about copyrights and related stuff have come up in the past though, so I have read a little bit on the subject to try to get an idea of things. When a user posts something on a forum (not just slinging.org, but any forum), that person holds the rights to their own words. This includes pictures, video, etc. Basically in the event of any legal situation, a user is responsible for what they post and not the forum. So no, slinging.org cannot grant use permission for any content posted by a member.
Content that already has a copyright is another matter. It's technically not legal to post copyrighted material on a forum. Unless of course you're the owner of it. That obviously does happen though (meaning copyrighted material getting posted). But I think for the vast majority of situations it's either unknown or ignored by the owner. As an example, if someone finds an image of a slinger on the Internet and posts it here, it's just for communication/entertainment purposes. No one is making money from it, or using it for advertising, etc. I'm not sure where a "fair use policy" might come into play, but maybe I just described it. Again, grain of salt for all the legal stuff.
All that aside, I ran a Google Image search on the picture. The earliest result it found is this one from 2013:
https://www.jpost.com/magazine/features/hot-off-the-arab-press-329593. In the linked article, the caption under the image reads
photo credit: REUTERS. I searched for Reuters and here is their website:
https://www.reuters.com/. You could try reaching out to these websites to inquire further about the image.
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