--- a/src/pyams_file/templates/picture.pt	Wed Oct 24 09:25:11 2018 +0200
+++ b/src/pyams_file/templates/picture.pt	Wed Oct 24 09:26:47 2018 +0200
@@ -1,11 +1,13 @@
 <picture
 	class="${css_class}"
 	tal:define="image_url tales:absolute_url(image);
-				timestamp tales:timestamp(image);">
+				thumbnails tales:thumbnails(image);">
 	<tal:if condition="xs_width">
 		<!-- xs source -->
 		<source media="(max-width: 767px)"
-				tal:define="width round(768 / 12 * xs_width)"
+				tal:define="width str(round(768 / 12 * xs_width));
+							thumb thumbnails.get_thumbnail(xs_thumb + ':w' + width);
+							timestamp tales:timestamp(thumb);"
 				srcset="${image_url}/++thumb++${xs_thumb}:w${width}?_=${timestamp}" />
 	</tal:if>
 	<source media="(max-width: 767px)"
@@ -14,7 +16,9 @@
 	<tal:if condition="sm_width">
 		<!-- sm source -->
 		<source media="(max-width: 991px)"
-				tal:define="width round(992 / 12 * sm_width)"
+				tal:define="width str(round(992 / 12 * sm_width));
+							thumb thumbnails.get_thumbnail(sm_thumb + ':w' + width);
+							timestamp tales:timestamp(thumb);"
 				srcset="${image_url}/++thumb++${sm_thumb}:w${width}?_=${timestamp}" />
 	</tal:if>
 	<source media="(max-width: 991px)"
@@ -23,7 +27,9 @@
 	<tal:if condition="md_width">
 		<!-- md source -->
 		<source media="(max-width: 1199px)"
-				tal:define="width round(1200 / 12 * md_width)"
+				tal:define="width str(round(1200 / 12 * md_width));
+							thumb thumbnails.get_thumbnail(md_thumb + ':w' + width);
+							timestamp tales:timestamp(thumb);"
 				srcset="${image_url}/++thumb++${md_thumb}:w${width}?_=${timestamp}" />
 	</tal:if>
 	<source media="(max-width: 1199px)"
@@ -32,7 +38,9 @@
 	<tal:if condition="lg_width">
 		<!-- lg source -->
 		<source media="(min-width: 1200px)"
-				tal:define="width round(1600 / 12 * lg_width)"
+				tal:define="width str(round(1600 / 12 * lg_width));
+							thumb thumbnails.get_thumbnail(lg_thumb + ':w' + width);
+							timestamp tales:timestamp(thumb);"
 				srcset="${image_url}/++thumb++${lg_thumb}:w${width}?_=${timestamp}" />
 	</tal:if>
 	<source media="(min-width: 1200px)"
@@ -40,5 +48,6 @@
 			srcset="/--static--/pyams_skin/img/dot.png" />
 	<!-- fallback image -->
 	<img style="width: 100%;"
+		 tal:define="timestamp tales:timestamp(image)"
 		 alt="${alt}" src="${image_url}?_=${timestamp}" />
 </picture>

--- a/src/pyams_file/thumbnail.py	Wed Oct 24 09:25:11 2018 +0200
+++ b/src/pyams_file/thumbnail.py	Wed Oct 24 09:26:47 2018 +0200
@@ -12,29 +12,25 @@
 
 __docformat__ = 'restructuredtext'
 
+import re
 
-# import standard library
-import re
 import transaction
-
-# import interfaces
-from pyams_file.interfaces import IImage, IThumbnails, IThumbnailer, IFileModifiedEvent, IWatermarker, IThumbnailFile
-from pyams_utils.interfaces.tales import ITALESExtension
+from BTrees import OOBTree
+from persistent.dict import PersistentDict
+from pyramid.events import subscriber
+from pyramid.threadlocal import get_current_registry
+from zope.interface import Interface, alsoProvides
+from zope.lifecycleevent import ObjectAddedEvent, ObjectCreatedEvent, ObjectRemovedEvent
+from zope.location import locate
 from zope.traversing.interfaces import ITraversable
 
-# import packages
-from BTrees import OOBTree
-from persistent.dict import PersistentDict
 from pyams_file.file import FileFactory
+from pyams_file.interfaces import IFileModifiedEvent, IImage, IThumbnailFile, IThumbnailer, IThumbnails, IWatermarker
 from pyams_file.zmi.image import render_image
 from pyams_utils.adapter import ContextAdapter, ContextRequestViewAdapter, adapter_config, get_annotation_adapter
+from pyams_utils.interfaces.tales import ITALESExtension
 from pyams_utils.registry import query_utility
 from pyams_utils.request import check_request
-from pyramid.events import subscriber
-from pyramid.threadlocal import get_current_registry
-from zope.interface import alsoProvides, Interface
-from zope.lifecycleevent import ObjectAddedEvent, ObjectRemovedEvent, ObjectCreatedEvent
-from zope.location import locate
 
 
 THUMBNAIL_ANNOTATIONS_KEY = 'pyams_file.image.thumbnails'
@@ -107,7 +103,7 @@
         geometries[selection_name] = geometry
         for current_thumbnail_name in list(self.thumbnails.keys()):
             if (current_thumbnail_name == selection_name) or \
-               current_thumbnail_name.startswith('{0}:'.format(selection_name)):
+                    current_thumbnail_name.startswith('{0}:'.format(selection_name)):
                 self.delete_thumbnail(current_thumbnail_name)
 
     def clear_geometries(self):
@@ -156,6 +152,13 @@
         # check for existing thumbnail
         if thumbnail_name in self.thumbnails:
             return self.thumbnails[thumbnail_name]
+        # check for selection thumbnail, in "selection:size" format
+        if ':' in thumbnail_name:
+            selection_name, size = thumbnail_name.split(':', 1)
+            selection = self.get_selection(selection_name)
+            if selection is not None:
+                thumbnails = IThumbnails(selection)
+                return thumbnails.get_thumbnail(size)
         # check for matching one
         name, size = self.get_thumbnail_name(thumbnail_name, with_size=True)
         if name: