In the common settings of IMCE, you can choose between
- Scale the image with respect to the thumbnail dimensions.
- First scale then crop the image to fit the thumbnail dimensions.

This choice is used for all thumbnail definitions as defined in the IMCE profile in the thumbnail section.

But what, if some of the thumbnails should be scaled while others should be scaled and then cropped?
Would it be possible to add an option to each thumbnail definition?

In the meantime, I have adjusted the imce_resize_image function inside of inc/imce.page.inc with the following code to override the setting for the 148x209 thumbnail definition:

  if ($width == 148 && $height == 209) {
    $op = 'scale_and_crop';

This works fine for me - but I hate overwriting modules... ;-)

Another solution would be to integrate the built in image styles of Drupal 7...

Many thanks!