How to add a thumbnail in a post in wordpress?

Question

I want to add thumbnails in the post in front page. But don't know how to do it. My theme do not support custom_field. one of the category's code is I pasted here.......

        <div class="featured">
        <h2>HEADLINES</h2>

            <!--This is where the thumbnails are found for the homepage bottom section - note the custom field name for this image is "thumbnail". Recommended image size is 70x70, as the stylesheet is written for this size.-->

            <?php $recent = new WP_Query("cat=3&showposts=3");  
          while($recent->have_posts()) : $recent->the_post();?>
        <?php the_post_thumbnail(); ?>

     <?php if( get_post_meta($post->ID, "thumbnail", true) ): ?>
                <a href="<?php the_post_thumbnail() ?>" rel="bookmark"><imgstyle="float:left;margin:0px 10px 0px 0px;" src="<?php echo get_post_meta($post->ID, "thumbnail", true); ?>" alt="alt text" /></a>
            <?php else: ?>
                <a href="<?php the_permalink() ?>" rel="bookmark"><imgstyle="float:left;margin:0px 10px 0px 0px;"  src="<?php bloginfo('template_url'); ?>/images/thumbnail.jp" alt="Default thumbnail" /></a>
            <?php endif; ?>             
            <b><a href="<?php the_permalink() ?>" ><?php the_title(); ?></a></b>
            <?php the_content_limit(80, ""); ?>

            <div style="border-bottom:1px dotted #AFAFAF; margin-bottom:10px; padding:0px 0px 10px 0px; clear:both;"></div>

            <?php endwhile; ?>

I rename the extension jpg to jp coz stackoverflow donot allow me to add image. I also changed

Answer 1

Prior to WordPress 2.9, thumbnails had to be custom fields. Since then, native support has been added.

Read about it on the Codex: http://codex.wordpress.org/Post_Thumbnails

In a nutshell, add this to your theme's functions.php file:

if ( function_exists( 'add_theme_support' ) ) { 
  add_theme_support( 'post-thumbnails' ); 
}

Then, add this to your theme where you want the thumbnail to appear:

<?php 
if ( has_post_thumbnail() ) { // check if the post has a Post Thumbnail assigned to it.
  the_post_thumbnail();
} 
?>

Answer 2

You can try this one.

http://wordpress.org/extend/plugins/wp-post-thumbnail

I didn't test it though. Thanks