Can anyone point me to the img_assist html code?

This is a themeable function, so what you can do, is copy the code of that function into the template.php file you have in your theme folder (if you have no template file like that, just create it, it's used for those exact things)

the code that you need to change is included here below:

change the following lines:

First, change the name of the function, replace 'theme' with the name of the theme you're using (i.e. bluemarine, if you're using that theme)

function theme_img_assist_inline($node, $size, $attributes) {

Next, change the lines where the caption is defined (remove the strong tags):

    $caption = '<strong>' . $attributes['title'] . ': </strong>' . $attributes['desc'];
  } elseif ($attributes['title']) {
    $caption = '<strong>' . $attributes['title'] . '</strong>';

And you're done :)

The original function:

function theme_img_assist_inline($node, $size, $attributes) {

  if ($attributes['title'] && $attributes['desc']) {
    $caption = '<strong>' . $attributes['title'] . ': </strong>' . $attributes['desc'];
  } elseif ($attributes['title']) {
    $caption = '<strong>' . $attributes['title'] . '</strong>';
  }
  $node->title = strip_tags($caption); // change the node title because img_assist_display() uses the node title for alt and title
  $img_tag = img_assist_display($node, $size);

  $output  = "<span class=\"inline {$attributes['align']}\">";
  $link = explode(',', $attributes['link']);

  if ($link[0] == 'node') {
    $output .= l($img_tag, "node/" . $node->nid, array(), NULL, NULL, FALSE, TRUE);

  } elseif ($link[0] == 'popup') {
    $popup_size = variable_get('img_assist_popup_label', 'preview');
    $info = image_get_info(file_create_path($node->images[$popup_size]));
    $width = $info['width'];
    $height = $info['height'];
    $output .= l($img_tag, '', array('onclick'=>"launch_popup($node->nid, $width, $height); return false;", 'target'=>'_blank'), NULL, NULL, FALSE, TRUE);

  } elseif ($link[0] == 'url') {
    $output .= l($img_tag, $link[1], array(), NULL, NULL, FALSE, TRUE);
  } else {
    $output .= $img_tag;
  }

  if ($caption) {
    $info = image_get_info(file_create_path($node->images[$size['label']]));
    $width = $info['width'] - 2; // reduce the caption width slightly so the variable width of the text doesn't ever exceed the image width
    $output .= "<span class=\"caption\" style=\"width: {$width}px;\">$caption</span>";
  }
  $output .= "</span>";
  return $output;
}

HTH
/elfur.is