if (get_option('medium_crop') === false) {
    add_option('medium_crop, '1');
} else {
    update_option('medium_crop', '1');
}

http://stackoverflow.com/questions/3454337/crop-thumbnail-to-exact-dimensions-on-wordpress-for-medium-size

Add this bit of code to functions.php

Crop medium thumbnail in WordPress

image, wordpress

PHP