How do I override recurring text/strings with icons/images?
Drupal allows you to override almost anything and what you are referring to here is the theme()ing of various pieces.  In your specific example, 'View' and 'Edit' are tabs/local tasks on a node page, and they are themed something like this in Drupal 6:

/**
 * Generate the HTML output for a single local task link.
 *
 * @ingroup themeable
 */
function theme_menu_local_task($link, $active = FALSE) {
  return '&lt;li '. ($active ? 'class="active" ' : '') .'&gt;'. $link ."&lt;/li&gt;\n";
} 


and this in Drupal 7:

/**
 * Returns HTML for a single local task link.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: A render element containing:
 *     - #link: A menu link array with 'title', 'href', and 'localized_options'
 *       keys.
 *     - #active: A boolean indicating whether the local task is active.
 *
 * @ingroup themeable
 */
function theme_menu_local_task($variables) {
  $link = $variables['element']['#link'];
  $link_text = $link['title'];

  if (!empty($variables['element']['#active'])) {
    // Add text to indicate active tab for non-visual users.
    $active = '&lt;span class="element-invisible"&gt;' . t('(active tab)') . '&lt;/span&gt;';

    // If the link does not contain HTML already, check_plain() it now.
    // After we set 'html'=TRUE the link will not be sanitized by l().
    if (empty($link['localized_options']['html'])) {
      $link['title'] = check_plain($link['title']);
    }
    $link['localized_options']['html'] = TRUE;
    $link_text = t('!local-task-title!active', array('!local-task-title' =&gt; $link['title'], '!active' =&gt; $active));
  }

  return '&lt;li' . (!empty($variables['element']['#active']) ? ' class="active"' : '') . '&gt;' . l($link_text, $link['href'], $link['localized_options']) . "&lt;/li&gt;\n";
}


So, to change this from text to a graphic, you would create a theme function of your own in your theme's template.php file:

function YOURTHEME_menu_local_task(....


that looked at either $link or $variables['#link'] and output an image instead of the text.

And if php isn't your forte, but jQuery is, you could also do it in the browser with something like:

$('.tabs a[href$="edit"]').html('&lt;img src="edit.jpg"&gt;');


which would replace the text of your edit link with an image.  If you went this route you would put this in a suitable drupal behavior wrapper in your theme or custom module as well.