I canít figure how to do Flickr.
Select your picture on Flickr. The picture will appear in a larger black rectangle. At the bottom right corner of that rectangle is a "Share" icon - it looks like a curving arrow pointing to the upper right. Click on that icon to display the share box. At the top of the share box click on the BBCode. Copy and paste the BBC into your post.
Note: Pasting the entire BBCode will add some text before and/or after your posted picture. If you want to eliminate that text, delete those parts of the BBCode that appear before the after the IMG code (i.e. before [img] and after [/img] before clicking on the Submit button for your post.