Flickr is a bit complicated, as it loves to insert a junk URL that, essentially, advertises their site. Here's a photo of mine at Flickr:
But to do that I had to go to the photo in my 'Photostream', click on it, click on the 'Share' icon (a curved arrow), select BBCode, and get this link:
[url=https://flic.kr/p/2o1jGc3][img]https://live.staticflickr.com/65535/52512188656_ab60d34d5e_c.jpg[/img][/url][url=https://flic.kr/p/2o1jGc3]Reference_Series_V[/url] by [url=https://www.flickr.com/photos/chrism229/]chrism229[/url], on Flickr
I then reduced that link in the Image box here by selecting and deleting everything after 'jpg' and everything before the second 'https' leaving just this:
https://live.staticflickr.com/65535/52512188656_ab60d34d5e_c.jpg
And the Image dialog here just puts the image tags [img][/img] around that address.
If you use Flickr's simple link, which the Flickr Share box helpfully calls 'Share' you get a link to the page with the image on, but not an image inline in a post here:
You'll get the hang of it!