is a WORDPRESS snippet
i found this nice snippet on the web but because i don`t know php i need some help.
This code extract the attached picture from post and display it as a shortcode. I dont wan`t to modify my template and insert [postimage] (-> the shortcode) in my index.php

function cwc_postimage($atts, $content = null) {
	extract(shortcode_atts(array(
		"size" => 'thumbnail',
		"float" => 'none'
	), $atts));
	$images =& get_children( 'post_type=attachment&post_mime_type=image&post_parent=' . get_the_id() );
	foreach( $images as $imageID => $imagePost )
	$fullimage = wp_get_attachment_image($imageID, $size, false);
	$imagedata = wp_get_attachment_image_src($imageID, $size, false);
	$width = ($imagedata[1]+2);
	$height = ($imagedata[2]+2);
	return '<div class="postimage" style="width: '.$width.'px; height: '.$height.'px; float: '.$float.';">'.$fullimage.'</div>';
}
add_shortcode("postimage", "cwc_postimage");

my thumbs have "thumb" on custom fields (i need to copy image url and paste it in the custom fileds -> below posts in wp dashbord) and i need help to modify that code and add "thumb" automaticaly on image extracted from this piece of code.

So, from what I've gathered from this post is you want something to do with 'thumb'(s). A thumb, as in a thumbnail? A thumb, as in the thing on your hand?

Do you want a watermark picture of a thumb on all your images? Or make thumbnails for all your images?

I don't understand the question.

no ... want to automatically add attached image url in my custom field for for front page thumbnail (thumb is custom field name)