Put a block in the sidebar, show untagged photos and ask for them to be tagged.

modules/tag_it/controllers/tag_it.php

@@ -0,0 +1,29 @@
+<?php defined("SYSPATH") or die("No direct script access.");
+/**
+ * Gallery - a web based photo album viewer and editor
+ * Copyright (C) 2000-2010 Bharat Mediratta
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or (at
+ * your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+class Tag_It_Controller extends Controller {
+  public function tags_for($id) {
+    $item = ORM::factory("item", $id);
+    access::required("view", $item);
+
+    $view = new View("tag_it_tags_for.html");
+    $view->tags = tag::item_tags($item);
+    print $view;
+  }
+}

modules/tag_it/helpers/tag_it_block.php

@@ -0,0 +1,67 @@
+<?php defined("SYSPATH") or die("No direct script access.");
+/**
+ * Gallery - a web based photo album viewer and editor
+ * Copyright (C) 2000-2010 Bharat Mediratta
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or (at
+ * your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+class tag_it_block_Core {
+  static function get_site_list() {
+    return array("untagged_photo" => t("Tag it"));
+  }
+
+  static function get($block_id, $theme) {
+    if (identity::active_user()->guest) {
+      return;
+    }
+
+    $block = "";
+    switch ($block_id) {
+    case "untagged_photo":
+      $attempts = 0;
+      do {
+        $item = item::random_query()
+          ->join("items_tags", "items.id", "items_tags.item_id", "left")
+          ->where("items.type", "!=", "album")
+          ->where("items_tags.item_id", "IS", null)
+          ->find_all(1)
+          ->current();
+      } while (!$item && $attempts++ < 3);
+      if ($item && $item->loaded()) {
+        $block = new Block();
+        $block->css_id = "g-tag-it-block";
+        $block->title = t("Tag it");
+        $block->content = new View("tag_it_block.html");
+        $block->content->item = $item;
+
+        $form = new Forge("tags/create/{$item->id}", "", "post",
+                          array("id" => "g-tag-it-add-tag-form", "class" => "g-short-form"));
+        $label = $item->is_album() ?
+          t("Add tag to album") :
+          ($item->is_photo() ? t("Add tag to photo") : t("Add tag to movie"));
+
+        $group = $form->group("add_tag")->label("Add Tag");
+        $group->input("name")->label($label)->rules("required")->id("name");
+        $group->hidden("item_id")->value($item->id);
+        $group->submit("")->value(t("Add Tag"));
+
+        $block->content->form = $form;
+      }
+      break;
+    }
+
+    return $block;
+  }
+}

modules/tag_it/module.info

@@ -0,0 +1,3 @@
+name = "Tag It"
+description = "Present an untagged photo and ask the user to tag it."
+version = 1

modules/tag_it/views/tag_it_block.html.php

@@ -0,0 +1,28 @@
+<?php defined("SYSPATH") or die("No direct script access.") ?>
+<script type="text/javascript">
+  $("#g-tag-it-add-tag-form").ready(function() {
+    $("#g-tag-it-add-tag-form input:text").autocomplete(
+      "<?= url::site("tags/autocomplete") ?>", {
+        max: 30,
+        multiple: true,
+        multipleSeparator: ',',
+        cacheLength: 1,
+        selectFirst: false,
+      }
+    );
+    $("#g-tag-it-add-tag-form").ajaxForm({
+      dataType: "json",
+      success: function(data) {
+        $("#g-tag-it-add-tag-form").resetForm();
+        $("#g-tag-it-tags-container").load("<?= url::site("tag_it/tags_for/{$item->id}") ?>");
+      }
+    });
+  });
+</script>
+<div class="g-tag-it-block">
+  <a href="<?= $item->url() ?>">
+   <?= $item->thumb_img(array("class" => "g-thumbnail")) ?>
+  </a>
+  <p id="g-tag-it-tags-container"></p>
+  <?= $form ?>
+</div>

modules/tag_it/views/tag_it_tags_for.html.php

@@ -0,0 +1,5 @@
+<?php defined("SYSPATH") or die("No direct script access.") ?>
+<?= t("Tags:") ?>
+<? foreach ($tags as $tag): ?>
+ <a href="<?= url::site("tag/{$tag->name}") ?>"><?= $tag->name ?></a>
+<? endforeach ?>