Read more about the usage of this script on http://ryanfitton.co.uk/blog/implementing-an-image-picker-for-wordpress-3-5/

WordPress 3.5 Functions.php Form Elements

<div style='clear:both;margin-bottom:10px;overflow:auto;'>
  <label>Image 1: </label>
	<input name='image_1_port' id='image_1_port' style='width:200px' />
	<input id='_btn' class='upload_image_button' type='button' value='Choose Image 1' />
</div>

<div style='clear:both;margin-bottom:10px;overflow:auto;'>
	<label>Image 2: </label>
	<input name='image_2_port' id='image_2_port' style='width:200px' />
	<input id='_btn' class='upload_image_button' type='button' value='Choose Image 2' />
</div>

<div style='clear:both;margin-bottom:10px;overflow:auto;'>
	<label>Image 3: </label>
	<input name='image_3_port' id='image_3_port' style='width:200px' />
	<input id='_btn' class='upload_image_button' type='button' value='Choose Image 3' />
</div>