How to get specific custom image size in template

Hi Sir,

I have some custom image sizes in my theme, like:

if ( function_exists( 'add_theme_support' ) ) {
	add_theme_support( 'post-thumbnails' );
	set_post_thumbnail_size( 220, 160, true ); // Normal post thumbnails
	add_image_size( 'small-image', 160, 160, true ); // Full size screen
	add_image_size( 'post-big-image', 618, 400, true ); // Full size screen
	add_image_size( 'original-image', 720, 540, true ); // Full size screen
	add_image_size( 'header-image', 940, 300, true ); // Full size screen
	add_image_size( 'vertical', 680, 907, false ); // Full size screen
}

I have custom post type “slide” for slideshow and there is custom field type image.

I want to print out in my theme “header-image” size of image.

My current code is:

<?php
					while ($my_query->have_posts()) : $my_query->the_post();
					$slidetitle = get_the_title();
					$slidetext = get_the_content();
					$slideimage = get_custom_field('bod_slide_image:to_image_src', 'header-image');
					$slidelink = get_post_meta($post->ID, bod_slide_link, true);
					?>
                    <li>
                    	<figure>
							<?php if( $slidelink ) : ?>
                            <a href="<?php echo $slidelink; ?>" title="<?php echo $slidetitle; ?>"><img src="<?php echo $slideimage; ?>" alt="<?php echo $slidetext; ?>" /></a>
                            <?php else : ?>
                            <img src="<?php echo $slideimage; ?>" alt="<?php echo $slidetext; ?>" />
                            <?php endif; ?>
                        </figure>
                    </li>
					<?php endwhile; ?>

This work if I crop image before upload.
It is possible, some how, to upload full image and then take specific size in theme.

http://wordpress.org/extend/plugins/custom-content-type-manager/