You can use "cropnail" - where I crop the image from the center and resize it to requested thumbnail size.
As long as your object is in the center, you will neither lose ratio nor lose the object.
Link: class.cropnail.inc.php: http://smarty-framework.googlecode.com/svn/trunk/library/classes/sanjaal/class.cropnail.inc.php
$cropnail = new cropnail(100, 200); # your target dimension
$cropnail->resize($original_image_filename, $cropnail_image_filename, 0);
This works irrespective of the dimension of your original image.
I mean to say: You can get a vertical cropnail from a horizontally oriented image.
You can have a 100x200 thumbnail from an image of 800x400 (see the changes in ratio).
And you still prevent the image being distorted.
This is not a normal way of creating thumbnails, but it works for me, hope for you too.