With Flickr, which I also use, each image has a the little share arrow (curves to the right). Click that arrow, select BBCode, select the image size you want, then copy the URL text. Paste that text here. That text contains more than the minimum required. So, I strip the extra text before/after the begin/end 'img' tags. You can then use the 'Preview' in the upper right of this text editor to see how it looks. Switch back to edit/adjust as needed until you are ready to post it.
Edit: Here is your image with the large (768 x 1024) size. Here is what that text looks like also after I took out the extra.
[img]https://live.staticflickr.com/65535/53368801798_a0f213407f_b.jpg[/img]