Here are modifications which make certain exif field useful also for tiff pictures, but must be checked and fixed for each and every field to be utilized.
This concerns the exif fields 'ImageDescription' and 'Copyright' only, which must be present in the $exif_info strings of 'exifmgr.php' and 'include/exif_php.inc.php' (lacked 'Copyright', I think). Next, change in 'include/exif_php.inc.php', at about l. 35:
// if ($size[2] != 2) {
if ($size[2] != 2 && $size[2] != 7) { // 2=jpeg, 7=tiff, accept both
Change in 'include/exif_php.inc.php', at about l. 50:
// $exifRawData = read_exif_data_raw($filename, 0);
// Use PHP native 'exif_read_data' function instead and arrange these fields
// in a 'IFD0' sub-array as does the 'read_exif_data_raw' CPG function:
$exifRawData = exif_read_data($filename);
$ifd0 = array('ImageDescription' => $exifRawData['ImageDescription'], 'Copyright' => $exifRawData['Copyright']);
$ifd0 = array('IFD0' => $ifd0);
$exifRawData = array_merge($exifRawData, $ifd0);
So, now these two exif fields are equally accessible for tiffs as jpegs!
And to sum up, the only remaining tiffy anomaly for me so far concerns show-original functionality. A quick way to a at least temporary solution is, for example, to make a link of the file name in the file information table, to be used as any picture link.
Hope this was informative for someone, and that full TIFF support will be included soon in Coppermine, perhaps including 'exif_read_data' of PHP?