If you click the link you posted go to the bottom RH corner of the pic and there is a RH arrow. Click that and then select BBcode in the popup. It also gives you options for the size of the photo. Just copy and paste that code into your post and you get this below.
20170718_152941 by
David Narens, on Flickr
If you look at the code that gets pasted into your post you can delete some of it if you just want a static photo without the link and info attached. Edit it down to the code below but replace the parenthesis I added on each end with a bracket [ at the beginning and ] at the end and you get the photo below the code. I had to change the brackets to parenthesis so the code would show instead of the picture.
(img]https://farm5.staticflickr.com/4330/35922886702_1ae4f829f0_z.jpg[/img)
Hope that helps explain how the code works. See the difference in the two?