images not showing despite using add_theme_support(‘post-thumbnails’);

Since you appear to be using Featured Images, replace this:

<div class="post-image">
    <?php echo ravs_get_custom_image( get_post_thumbnail_id () ); ?>
</div><!-- end post-image -->

with this:

<div class="post-image">
    <?php
        if ( has_post_thumbnail() ) {
            the_post_thumbnail( 'custom-image' );
        }
    ?>
</div>

References

Codex:
has_post_thumbnail()
the_post_thumbnail()