A modified version of this, which both accepts image links and interwiki-image-links for descriptions, as well as option to loose the brackets are included in version 0.25 --EvenHolen

Images as references

If you want that an image becomes a link exactly like a usual description reference,

or in other words, that the text

[http://tavi.sourceforge.net/WikkiTikkiTavi http://tavi.sourceforge.net/tavi.png]

becomes the image link in the top-right corner of this page,

apply the patch below to your Tavi 0.22 sources

(this one works fine on main image of the french site http://wikira.tuxfamily.org).

Return to TaviPatches.

In parse/transforms.php

Replace the portion of code

function parse_hyperlink_description($text)
{
  global $UrlPtn;

  return preg_replace("/\\[($UrlPtn) ([^]]+)]/e",
                      "url_token(q1('\\1'), q1('[\\4]'))", $text, -1);
}

with this one

function parse_image_ref($text)
{
  if (preg_match('/(.jpe?g|.png|.gif|.bmp)$/i', $text))
  {
    return preg_replace('/(http:\/\/)([A-Za-z0-9\\/?=&~_.\-]*)(jpe?g|png|gif|bmp)/',
                        '<img src="\\1\\2\\3" border="0">', $text, -1);
  }
  else
  {
    return '[' . $text . ']';
  }
}

function parse_hyperlink_description($text)
{
  global $UrlPtn;

  $str = preg_replace("/\\[($UrlPtn) ([^]]+)]/e",
                        "url_token(q1('\\1'), q1(parse_image_ref('\\4')))", $text, -1);
  return $str;
}

Please, don't hesitate to critic my code below this line --LaurentJacques

If you would also like the benefit of TaviPatches/ExternalLinks simply substitute the above line:

    return '[' . $text . ']';

with 

    return $text;

-- John-Mason P. Shackelford

In the code q1(parse_image_ref('\\4')))", $text, -1), the 4 should be replaced by 2. (it probably refers to the statement's number in an [ ] (array))
This also goes for the original code (at least up to 0.24).

Thor.