Here it is...
Flickr_Share by
Ron Lowe, on Flickr
Click it, and select BBcode in the list of options.
Select Medium in the drop-down.
Click in the box of text which contans the generated BBcode,it will turn blue.
Press Ctrl-C to copy the highlighted text.
Thusly:
Flickr_Share1 by
Ron Lowe, on Flickr
Click into your post on yacf, and press ctrl-V to paste the BBcode into your post.
This will post something like this into your message:
[u
rl=https://flic.kr/p/PUtSQ3][i
mg]https://farm2.staticflickr.com/1941/31442664898_0e90d4a5bb_z.jpg[/img][/url][u
rl=https://flic.kr/p/PUtSQ3]Flickr_Share1[/url] by [u
rl=https://www.flickr.com/photos/62966413@N04/]Ron Lowe[/url], on Flickr
The forum code will automagically parse that out and display the image.