Disable Responsive Image Sizes crop

If you mean you want to only save the original image to the server, and not have WP auto-generate additional sizes, there’s a function to remove the additional sizes:

<?php
function wpse_remove_image_sizes() {
    // Remove the WP Core "thumbnail" size
    remove_image_size( 'thumbnail' );
    // Remove a custom image size with the slug "custom-size-name"
    remove_image_size( 'custom-size-name' );
    // Add any other sizes you need to remove -
    // this will depend on your theme and plugins.
}
add_action('init', 'wpse_remove_image_sizes');
?>

Proceed with caution, because many themes and some plugins use these other sizes, particularly the thumbnail.