Gets an img tag for an image attachment, scaling it down if requested.

The {@see ‘get_image_tag_class’} filter allows for changing the class name for the
image without having to use regular expressions on the HTML content. The
parameters are: what WordPress will use for the class, the Attachment ID,
image align value, and the size the image should be.

The second filter, {@see ‘get_image_tag’}, has the HTML content, which can then be
further manipulated by a plugin to change all attribute values and even HTML
content.

function get_image_tag( $id, $alt, $title, $align, $size = 'medium' ) {

	list( $img_src, $width, $height ) = image_downsize( $id, $size );
	$hwstring                         = image_hwstring( $width, $height );

	$title = $title ? 'title="' . esc_attr( $title ) . '" ' : '';

	$size_class = is_array( $size ) ? implode( 'x', $size ) : $size;
	$class      = 'align' . esc_attr( $align ) . ' size-' . esc_attr( $size_class ) . ' wp-image-' . $id;

	/**
	 * Filters the value of the attachment's image tag class attribute.
	 *
	 * @since 2.6.0
	 *
	 * @param string       $class CSS class name or space-separated list of classes.
	 * @param int          $id    Attachment ID.
	 * @param string       $align Part of the class name for aligning the image.
	 * @param string|int[] $size  Requested image size. Can be any registered image size name, or
	 *                            an array of width and height values in pixels (in that order).
	 */
	$class = apply_filters( 'get_image_tag_class', $class, $id, $align, $size );

	$html = '';

	/**
	 * Filters the HTML content for the image tag.
	 *
	 * @since 2.6.0
	 *
	 * @param string       $html  HTML content for the image.
	 * @param int          $id    Attachment ID.
	 * @param string       $alt   Image description for the alt attribute.
	 * @param string       $title Image description for the title attribute.
	 * @param string       $align Part of the class name for aligning the image.
	 * @param string|int[] $size  Requested image size. Can be any registered image size name, or
	 *                            an array of width and height values in pixels (in that order).
	 */
	return apply_filters( 'get_image_tag', $html, $id, $alt, $title, $align, $size );
}