Creating images in your templates in drupal 7 is somewhat different, so here is the code
<?php
$hero_image = array(
'style_name' => 'case_study_teaser',
'path' => $image['uri'],
'width' => '',
'height' => '',
'alt' => $image['alt'],
'title' => $image['title'],
);
print theme('image_style',$hero_image);
$img_url = 'public://myimagefolder/imgfilename.jpg'; // the orig image uri
$style = 'thumbnail'; // or any other custom image style you've created via /admin/config/media/image-styles
?>
<img src="<?php print image_style_url($style, $img_url) ?>>
For some more info, check examples here http://benbuckman.net/tech/11/04/how-render-image-fields-drupal-7