If you link an image in a forum post that has nothing to do with our program or any permissions since you are not even in our program. Your in your forum and your linking a direct url to an image so there is no permission to apply from the gallery. You can only apply permissions when your running an application and viewing say the image through scripting.
These images in forum posts would have always been visible in any version because you or your users are linking images like this
[ img ] some direct url to an image [ /img ]
Obviously no spaces but that is how forum bbcode works and has nothing to do with an application it has to be a direct url to an image.
No not to my knowledge because using bcode on a forum requires to my knowledge a direct full url to an image. You can not use script links to my knowledge. Using full direct urls to an image your calling the image directly from the server which is outside of your gallery or its permissions. It is possible for permissions to be applied if you where using script links to images using watermark.php to serve the image however you have not been able to use script links in forum bbcode for over a decade as its a security risk which is why no forum allows you to link scripting directly.