Same issue happening for me today on our post
SharkGate ICO . Some people mentioned it on our launch page and actually, all the images were loading for me but when I cleared cache, so my browser was loading the image fresh, then it was happening on that posts and all the other ones I have looked at since. I believe the forum is having a blip today on image loading. A CDN issue etc ? Actually looking around I see on older posts this has happened before on the forum. Expect they will solve it soon as must be getting lots of mentions of it. On a side note, it would be good if the SMF was upgraded to the latest version as I believe version 1.1.19 is known to contain a few nasty vulnerabilities (I have not checked the site source though to confirm it is 1.1.19, maybe there is just an older version number in the footer).