Try using has_term(). Something like this:
<?php if( has_term('term1', 'taxonomy_name', $post) ) { ?>
<img src="http://www.site.com/wp-content/themes/site/img/stars-01.png" width="100" height="21" alt="default">
<?php }elseif ( has_term( 'term2', 'taxonomy_name', $post) ) { ?>
<img src="http://www.site.com/wp-content/themes/site/img/stars-01.png" width="100" height="21" alt="default">
<?php } else { ?>
<img src="http://www.site.com/wp-content/themes/site/img/stars-01.png" width="100" height="21" alt="default">
<?php } ?>
You may also want to try using shorthand if/else statements, it tends to make the code a little cleaner and easier to read in situations like like this.
Same example using shorthand:
<?php if( has_term('term1', 'taxonomy_name', $post) ): ?>
<img src="http://www.site.com/wp-content/themes/site/img/stars-01.png" width="100" height="21" alt="default">
<?php elseif ( has_term( 'term2', 'taxonomy_name', $post) ) :?>
<img src="http://www.site.com/wp-content/themes/site/img/stars-01.png" width="100" height="21" alt="default">
<?php else: ?>
<img src="http://www.site.com/wp-content/themes/site/img/stars-01.png" width="100" height="21" alt="default">
<?php endif; ?>
Hope this helps!