Attached is an image of what I'm trying to accomplish, with the location of the custom field in red, in the main frame of the picture, below the title and caption.
A link to your coppermine-driven gallery might help as well
Not a frame. In web-terms, frame refers to the use of a particular HTML element. If you just want to add some text there, you'll need to modify themes/yourtheme/theme.php. Find
$template_display_media
and edit the section as you see fit. If the section doesn't exist in your custom theme, copy the section
// HTML template for intermediate image display
$template_display_media = <<<EOT
<tr>
<td align="center" class="display_media" nowrap="nowrap">
<table cellspacing="2" cellpadding="0" class="imageborder">
<tr>
<td align="center">
{IMAGE}
</td>
</tr>
</table>
</td></tr>
<tr><td>
<table width="100%" cellspacing="2" cellpadding="0" class="tableb">
<tr>
<td align="center">
{ADMIN_MENU}
</td>
</tr>
</table>
<!-- BEGIN img_desc -->
<table cellpadding="0" cellspacing="0" class="tableb" width="100%">
<!-- BEGIN title -->
<tr>
<td class="tableb"><center><b>
{TITLE}
</b></center></td>
</tr>
<!-- END title -->
<!-- BEGIN caption -->
<tr>
<td class="tableb"><center>
{CAPTION}
</center></td>
</tr>
<!-- END caption -->
</table>
<!-- END img_desc -->
</td>
</tr>
EOT;
from themes/sample/theme.php into a new line before
?>
into themes/yourtheme/theme.php
If you want to actually add the content of a custom field (i.e. data pulled from the database), you'll have to come up with a more complicated hack. It would be easier if you would have done as suggested and posted a link and additional details what you actually want to see acomplished.
Where is a good place to find these mods of which you've spoken?
Filter & Sort File Information Fields on Image Display Page