The code for that is [img]http://sharefile.i2p/file/f0/f0...71/unknown.png[/img]
However, for small images like this 96-byte masterpiece, there is little reason to create an entire additional external request, when a perfectly valid protocol to inline images already exists:
[img]data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAcAAAAHAQMAAAD+nMWQAAAABlBMVEUAAAD///+l2Z/dAAAAFUlEQVR4XmP4x3CN4R8Q7mI4xvAPACz4Bk8WQsVUAAAAAElFTkSuQmCC[/img]
This is the entire image. If the text "data:" would not be filtered it would be easy to include small images.
here is a clearnet thread about how to allow those "links".
https://www.phpbb.com/community/viewtopic.php?t=2606271