WordPress Conditions

At the relevant point in the theme template, something like this:

<?php
   if( is_page( array( 1, 2, 3 ) ) ) :
      $img_link = "http://www.example.com/test";
   else :
      $img_link = "http://www.example.com";
   endif;
?>
<a href="<?php echo $img_link; ?>"><img src="hello-world.png" width="400" height="400" alt="Hello world" /></a>