Add this code to your functions.php
if(function_exists('add_theme_support'))
add_theme_support('post-thumbnails');
// Set the thumbnail size
add_image_size('custom_logo', 200, 200, true );
add_image_size('custom_website_thumb', 450, 200, true );
add_image_size('custom_print_ad_thumb', 200, 400, true );
Put this in your post template where you want to see the image.
<?php echo get_the_post_thumbnail($post_id, 'custom_logo'); ?>
You can also wrap it in a link like this.
<a href="https://wordpress.stackexchange.com/questions/36677/<?php echo get_permalink($post_id) ?>" title="<?php echo get_the_title($post_id); ?>"> <?php echo get_the_post_thumbnail($post_id, 'custom_logo'); ?></a>
You can see the WordPress Codex for more exploitation.
Remember to set the images as a featured image on upload to be able to use it.