• Go to to the flickr stream: https://www.flickr.com/photos/79844933@N08/?hide_photostream_welcome=1
• Choose your image and click the “share” arrrow
• Choose HTML embed and choose what size you want to embed it as
• Copy the embed code
• Paste that code into your wiki page
• Extract the source of the image from that HTML. It should look something like this:
  
• This is the part that matters to you: https://farm1.staticflickr.com/691/21175808538_28b1436aee.jpg>
•  Paste your source URL into this code snippet
  https://farm1.staticflickr.com/691/21175808538_28b1436aee.jpg

Example:

https://farm6.staticflickr.com/5804/21362448975_0df5aa5ca7.jpg

For more information about using images in mediawiki go here: https://www.mediawiki.org/wiki/Help:Images