WordPress at a glance
filter is not described

wp_check_filetype_and_ext filter-hook . WP 3.0.0

Filters the "real" file type of the given file.

Usage

add_filter( 'wp_check_filetype_and_ext', 'filter_function_name_3446', 10, 4 );
function filter_function_name_3446( $wp_check_filetype_and_ext, $file, $filename, $mimes ){
	// filter...

	return $wp_check_filetype_and_ext;
}
$wp_check_filetype_and_ext(array)
File data array containing 'ext', 'type', and 'proper_filename' keys.
$file(string)
Full path to the file.
$filename(string)
The name of the file (may differ from $file due to $file being in a tmp directory).
$mimes(array)
Key is the file extension with value as the mime type.

Where the hook is called

wp_check_filetype_and_ext()
wp-includes/functions.php 2413
return apply_filters( 'wp_check_filetype_and_ext', compact( 'ext', 'type', 'proper_filename' ), $file, $filename, $mimes );

Where the hook is used (in WP core)

Does not used.