Plugin Image Cropper — WordPress.com

For cropping a post thumbnail image to 200×300 pixels:

<?php
    the_post();
    img(200, 300);
?>

This will verify the existence of post thumbnail, crop the image, save it in uploads folder, and generate an image tag.

To verify the existence of a post thumbnail, you can use has_img()

<?php if (has_img()): ?>
<figure>
    <?php img(200, 300) ?>
    <figcaption>Some text</figcaption>
</figure>
<?php endif ?>

To crop images that are not post thumbnails, you can use crop($url, $size)

<?php
    $cropped_url= crop( get_bloginfo('url') . '/wp-content/uploads/image.jpg', array(200, 300) );
?>
<img src="<?php echo $cropped_url ?>">

Image Cropper