Aardvark

This theme uses WordPress's native image resize function add_image_size(). You can edit the theme's predefined image sizes by adding the following code to your child theme's functions.php file. You can change the image width, height and cropping options (including cropping position) for any of the image sizes. You will then need to run the Regenerate Thumbnails plugin after uploading these changes to recrop all your images to the new dimensions.

function ghostpool_image_sizes() {                
    add_image_size( 'gp_small_image', 75, 75, true );
    add_image_size( 'gp_list_image', 250, 135, true );
    add_image_size( 'gp_square_image', 300, 300, true );
    add_image_size( 'gp_featured_image', 864, 467, true );
    add_image_size( 'gp_column_image', 727, 393, true );
    add_image_size( 'gp_related_image', 414, 224, true );
    add_image_size( 'gp_featured_box_small_image', 330, 240, true );    
    add_image_size( 'gp_featured_box_large_image', 600, 480, true );    
    add_image_size( 'gp_featured_box_full_image', 1260, 480, true );            
}

If you want to add your own image sizes to the selection, instead of changing a predefined image, add the following code to your child theme's functions.php file and add your new image sizes as shown below:

function ghostpool_register_new_image_sizes() {          
    add_image_size( 'ghostpool-new-image-name-1', 100, 100, true );
    add_image_size( 'ghostpool-new-image-name-2', 500, 900, false );              
}
add_action( 'after_setup_theme', 'ghostpool_register_new_image_sizes' );