Source

File: wp-admin/includes/image.php

function file_is_displayable_image( $path ) {
	$displayable_image_types = array( IMAGETYPE_GIF, IMAGETYPE_JPEG, IMAGETYPE_PNG, IMAGETYPE_BMP, IMAGETYPE_ICO );

	$info = @getimagesize( $path );
	if ( empty( $info ) ) {
		$result = false;
	} elseif ( ! in_array( $info[2], $displayable_image_types, true ) ) {
		$result = false;
	} else {
		$result = true;
	}

	/**
	 * Filters whether the current image is displayable in the browser.
	 *
	 * @since 2.5.0
	 *
	 * @param bool   $result Whether the image can be displayed. Default true.
	 * @param string $path   Path to the image.
	 */
	return apply_filters( 'file_is_displayable_image', $result, $path );
}