Function to get thumbnail img source

Question

I have this function call that displays an entire img tag with the correct url for that post.. the thumbnail img...

?php the_post_thumbnail('blog-page'); ?>

What I need is just the source address for that img.

How can I get that source dynamically?

---

Here is a little more explanation of what it is exaclty that I'm doing...

This is the code that displays the thumbnail for a page in my wordpress:

<div class="entry-thumbnail">
<a rel="lightbox" href="<?php the_permalink(); ?>"><?php the_post_thumbnail('blog-page'); ?></a>
</div> 

I need that a tag's href to use the img's source instead of linking to the blog post it's self to get lightbox to work properly.

Answer 1

wp_get_attachment_url( get_post_thumbnail_id($post->ID) );

all together:

    <div class="entry-thumbnail">
       <a rel="lightbox" href="<?php echo wp_get_attachment_url( get_post_thumbnail_id($post->ID) ); ?>"><?php echo get_the_post_thumbnail( $post->ID ); ?></a>
    </div> 

Answer 2

In your code you use the_post_thumbnail('blog-page') where 'blog-page' is a custom image size previous registered with add_image_size. So, if you want control thumbnail size, try this:

<?php
global $post;
$imageid = get_post_thumbnail_id( $post->ID );
$image_thumb = wp_get_attachment_image_src( $imageid, 'blog-page' );
$image_url = wp_get_attachment_url( $imageid );
/*
if you want to control image size also for lightbox (useful for very big images) use instead:
$image_large = wp_get_attachment_image_src( $imageid, 'large' );
$image_url = $image_large[0];
*/
?>

<div class="entry-thumbnail">
   <a rel="lightbox" href="<?php echo $image_url; ?>">
       <img src="<?php echo $image_thumb[0]; ?>" alt="<?php the_title(); ?>" />
   </a>
</div>