diff --git a/modules/admin/lang/en.php b/modules/admin/lang/en.php
index 19e7231a0..346aab137 100644
--- a/modules/admin/lang/en.php
+++ b/modules/admin/lang/en.php
@@ -338,8 +338,9 @@ $lang->mobile_viewport = 'Mobile viewport Setting';
 $lang->about_mobile_viewport = 'The settings entered above will be output in a <meta name="viewport"> tag for mobile visitors.';
 $lang->restore_default_viewport = 'Restore Default';
 $lang->thumbnail_target = 'Extract Thumbnail From';
-$lang->thumbnail_target_all = 'All images';
+$lang->thumbnail_target_content = 'All embedded images, including external images';
 $lang->thumbnail_target_attachment = 'Attached images only';
+$lang->about_thumbnail_target = 'Using external images to generate thumbnails may cause various issues with respect to page load speed, copyright, and security. Please be careful.';
 $lang->thumbnail_type = 'Thumbnail Type';
 $lang->input_header_script = 'Header Script';
 $lang->detail_input_header_script = 'Content added here will be printed at the top of every page, except the admin module.';
diff --git a/modules/admin/lang/ko.php b/modules/admin/lang/ko.php
index 5c0f39257..d03a4e08c 100644
--- a/modules/admin/lang/ko.php
+++ b/modules/admin/lang/ko.php
@@ -334,8 +334,9 @@ $lang->mobile_viewport = '모바일 viewport 설정';
 $lang->about_mobile_viewport = '모바일 접속시 여기 입력한 내용이 <meta name="viewport"> 태그로 출력됩니다.';
 $lang->restore_default_viewport = '기본값 복원';
 $lang->thumbnail_target = '썸네일 생성 대상';
-$lang->thumbnail_target_all = '모든 이미지 (외부 이미지 포함)';
+$lang->thumbnail_target_content = '모든 이미지 (외부 이미지 포함)';
 $lang->thumbnail_target_attachment = '첨부된 이미지';
+$lang->about_thumbnail_target = '외부 이미지를 사용하여 썸네일을 생성하는 경우 페이지 로딩 속도, 저작권, 보안 등 다양한 문제가 발생할 수 있으니 주의하시기 바랍니다.';
 $lang->thumbnail_type = '썸네일 생성 방식';
 $lang->input_header_script = '상단(헤더) 스크립트';
 $lang->detail_input_header_script = '모든 페이지의 최상단에 코드를 삽입합니다. 관리자 화면에는 적용되지 않습니다.';
diff --git a/modules/admin/tpl/config_advanced.html b/modules/admin/tpl/config_advanced.html
index 154ec1eb3..c1c158476 100644
--- a/modules/admin/tpl/config_advanced.html
+++ b/modules/admin/tpl/config_advanced.html
@@ -130,14 +130,15 @@
 					<input type="radio" name="thumbnail_target" id="thumbnail_target_attachment" value="attachment" checked="checked"|cond="$thumbnail_target == 'attachment' || !$thumbnail_target" />
 					{$lang->thumbnail_target_attachment}
 				</label>
-				<label for="thumbnail_target_all" class="x_inline">
-					<input type="radio" name="thumbnail_target" id="thumbnail_target_all" value="all" checked="checked"|cond="$thumbnail_target == 'all'" />
-					{$lang->thumbnail_target_all}
+				<label for="thumbnail_target_content" class="x_inline">
+					<input type="radio" name="thumbnail_target" id="thumbnail_target_content" value="content" checked="checked"|cond="$thumbnail_target == 'content'" />
+					{$lang->thumbnail_target_content}
 				</label>
 				<label for="thumbnail_target_none" class="x_inline">
 					<input type="radio" name="thumbnail_target" id="thumbnail_target_none" value="none" checked="checked"|cond="$thumbnail_target == 'none'" />
 					{$lang->thumbnail_none}
 				</label>
+				<p class="x_help-block">{$lang->about_thumbnail_target}</p>
 			</div>
 		</div>
 		<div class="x_control-group">
diff --git a/modules/document/document.model.php b/modules/document/document.model.php
index 087e8fec7..d036807b4 100644
--- a/modules/document/document.model.php
+++ b/modules/document/document.model.php
@@ -1037,7 +1037,7 @@ class DocumentModel extends Document
 		{
 			self::$_config = ModuleModel::getModuleConfig('document') ?: new stdClass;
 		}
-		if (!isset(self::$_config->thumbnail_target))
+		if (!isset(self::$_config->thumbnail_target) || self::$_config->thumbnail_target === 'all')
 		{
 			self::$_config->thumbnail_target = 'attachment';
 		}