Go to your vid on YT.
Find the Share icon under the vido.
Click Share.
Click Copy.
Go to 8Kun.
Click the blue arrow .
Post your copied link from YT Share option.
Usually when I get that message, the vid or image posts anyway. I know what you're talking about though. Sometimes stuff will do that, and post…but there will be no (You) marking your post.
Either I bear with it, or I might get rid of all open tabs and clear cache.
Restart browser or even my whole rig and then go ahead and solve Captcha again.
Sometimes that does it.