It's somewhat well-known how to add custom media sizes by using:
add_image_size( HANDLE, WIDTH, HEIGHT, CROP );
But, how to remove them? I've added a "tiny" 50x50 size and now my post-thumbnail-meta-box uses it to show the thumbnail. I only could override this by setting default thumbnail again with:
set_post_thumbnail_size(get_option('thumbnail_size_w'), get_option('thumbnail_size_h'), get_option('thumbnail_crop'));
Can somebody help me?