Source

File: wp-includes/deprecated.php

function get_attachment_icon( $id = 0, $fullsize = false, $max_dims = false ) {
	_deprecated_function( __FUNCTION__, '2.5.0', 'wp_get_attachment_image()' );
	$id = (int) $id;
	if ( !$post = get_post($id) )
		return false;

	if ( !$src = get_attachment_icon_src( $post->ID, $fullsize ) )
		return false;

	list($src, $src_file) = $src;

	// Do we need to constrain the image?
	if ( ($max_dims = apply_filters('attachment_max_dims', $max_dims)) && file_exists($src_file) ) {

		$imagesize = @getimagesize($src_file);

		if (($imagesize[0] > $max_dims[0]) || $imagesize[1] > $max_dims[1] ) {
			$actual_aspect = $imagesize[0] / $imagesize[1];
			$desired_aspect = $max_dims[0] / $max_dims[1];

			if ( $actual_aspect >= $desired_aspect ) {
				$height = $actual_aspect * $max_dims[0];
				$constraint = "width='{$max_dims[0]}' ";
				$post->iconsize = array($max_dims[0], $height);
			} else {
				$width = $max_dims[1] / $actual_aspect;
				$constraint = "height='{$max_dims[1]}' ";
				$post->iconsize = array($width, $max_dims[1]);
			}
		} else {
			$post->iconsize = array($imagesize[0], $imagesize[1]);
			$constraint = '';
		}
	} else {
		$constraint = '';
	}

	$post_title = esc_attr($post->post_title);

	$icon = "<img src='$src' title='$post_title' alt='$post_title' $constraint/>";

	return apply_filters( 'attachment_icon', $icon, $post->ID );
}