How to get taxonomy image and path by tid in Drupal 7?
I'm guessing you're looking for something like:

$term = taxonomy_term_load($tid);
if ($image_items = field_get_items('taxonomy_term', $term, 'field_name')) {
  $uri = $image_items[0]['uri'];
  $external_url = file_create_url($uri);
}


Where field_name is replaced with the name of your image field.