by Son of a Beach » Mon 06 Apr, 2020 1:13 pm
If you have a look at the main Gallery forum page, you will see two announcement topics near the top of the page (above the main list of topics). One with instructions for uploading photos (this is where there is a limit on how many photos you can upload) and one with instructions on how to embed photos that are already hosted somewhere on the internet. Although this second topic says, "other sites", it applies equally well to photos that are already hosted on this site in other topics.
Take a look at it, and see if it makes sense. If not, let us know where you're getting stuck.
In short, the key is (as that post says): In the text of your new forum post, reference [the hosted image] in the format: [img]URL[/img]
(replacing 'URL' with the actual internet URL of your image file).
There is also an "Img" button in the forum post editor to help with this.
(NB: I'm not an admin on this site, but I did write those two topics, many years ago.)