TYPO3 Core

I don't know since when this feature is in the core, but is quite handy to have thumbnails of images in the list module.

But the implementation in DatabaseRecordList is buggy:

// Render thumbnails, if:
// - a thumbnail column exists
// - there is content in it
// - the thumbnail column is visible for the current type
$typeColumn = $GLOBALS['TCA'][$table]['ctrl']['type'];
$type = $row[$typeColumn];
$visibleColumns = $GLOBALS['TCA'][$table]['types'][$type]['showitem'];

This code fails for all tables that don't have a type column and will probably trigger some notices when it accesses $GLOBALS['TCA'][$table]['ctrl']['type']

How to test:
adding "'thumbnail' => 'images'," to the ctrl part of a table should get you a preview for the images column in the list module, if the field is shown for the current type.

If no type field is set at all, FormEngine checks for type 0 and 1 as a fallback, so this should be implemented in DatabaseRecordList as well:

// If current typeNum doesn't exist, set it to 0 (or to 1 for historical reasons, if 0 doesn't exist)
if (!$GLOBALS['TCA'][$table]['types'][$typeNum]) {
    $typeNum = $GLOBALS['TCA'][$table]['types']['0'] ? 0 : 1;
}

It is also documented in http://docs.typo3.org/typo3cms/TCAReference/Reference/Ctrl/Index.html , so fixing this is no new feature!