The Society no longer host images for members on their servers. To post an Image in the forum you need to host your image on a server on the Internet. Examples of free servers are imgur.com , Google Drive, Dropbox, Flickr etc.
if you click on the image in the forum you shall see:
added to your post.
Insert the URL of the image between the ][ ,
e.g. [img]https://imgur.com/abc def/1234.jpg[/img] and your post will include the image when it is posted or previewed.