theme

If you have an image style specified in Drupal 7 and you'd like to programmatically render an image thumb nail with that image style, try something like this:

$image = theme(
  'image_style',
  array(
    'path' => 'public://my_example_image.jpg',
    'style_name' => 'my_custom_image_style',
    'alt' => 'Alternate Text',
    'title' => 'Title Text',
  )
);
print $image;

This would work if you had an image style specified at admin/config/media/image-styles that was called 'my_custom_image_style'.

To theme the exposed filter form on a view in Drupal: