diff -r 5ac0fcedd89e -r 46d1f7b3d3bb src/pyams_content/component/gallery/zmi/templates/gallery-medias.pt
--- a/src/pyams_content/component/gallery/zmi/templates/gallery-medias.pt	Tue Jul 10 13:35:28 2018 +0200
+++ b/src/pyams_content/component/gallery/zmi/templates/gallery-medias.pt	Tue Jul 10 14:10:19 2018 +0200
@@ -49,8 +49,9 @@
 												 image_size thumbnail.get_image_size();
 												 margin_left 64 - image_size[0] / 2;
 												 margin_top 64 - image_size[1] / 2;
-												 title i18n:media.title;"
-									 tal:attributes="src tales:absolute_url(thumbnail);
+												 title i18n:media.title;
+												 src tales:absolute_url(thumbnail);"
+									 tal:attributes="src string:${src}?_=${tales:timestamp(thumbnail)};
 													 id 'media_{0}_{1}'.format(context.__name__, media.__name__);
 													 original-title title or '--';
 													 style string:margin-left: ${margin_left}px;; margin-right: ${margin_left}px;; margin-top: ${margin_top}px;; margin-bottom: ${margin_top}px;;" />