Thank you again! I found the solution!
I tried to edit code to use unique image size, but its not working.
I added to functions.php:
if ( function_exists( 'add_image_size' ) ) {
add_image_size( 'sidebar-thumb', 200, 120, true );
}
Everything ok, it generates the new image with the good size but when I change the ‘thumbnail’ to ‘sidebar-thumb’ nothing change. Whats wrong?