diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -2557,6 +2557,7 @@
     'PhabricatorFileHasObjectEdgeType' => 'applications/files/edge/PhabricatorFileHasObjectEdgeType.php',
     'PhabricatorFileIconSetSelectController' => 'applications/files/controller/PhabricatorFileIconSetSelectController.php',
     'PhabricatorFileImageMacro' => 'applications/macro/storage/PhabricatorFileImageMacro.php',
+    'PhabricatorFileImageProxyController' => 'applications/files/controller/PhabricatorFileImageProxyController.php',
     'PhabricatorFileImageTransform' => 'applications/files/transform/PhabricatorFileImageTransform.php',
     'PhabricatorFileInfoController' => 'applications/files/controller/PhabricatorFileInfoController.php',
     'PhabricatorFileLinkView' => 'view/layout/PhabricatorFileLinkView.php',
@@ -7379,6 +7380,7 @@
       'PhabricatorTokenReceiverInterface',
       'PhabricatorPolicyInterface',
     ),
+    'PhabricatorFileImageProxyController' => 'PhabricatorFileController',
     'PhabricatorFileImageTransform' => 'PhabricatorFileTransform',
     'PhabricatorFileInfoController' => 'PhabricatorFileController',
     'PhabricatorFileLinkView' => 'AphrontView',
diff --git a/src/applications/files/application/PhabricatorFilesApplication.php b/src/applications/files/application/PhabricatorFilesApplication.php
--- a/src/applications/files/application/PhabricatorFilesApplication.php
+++ b/src/applications/files/application/PhabricatorFilesApplication.php
@@ -78,7 +78,7 @@
         'delete/(?P<id>[1-9]\d*)/' => 'PhabricatorFileDeleteController',
         'edit/(?P<id>[1-9]\d*)/' => 'PhabricatorFileEditController',
         'info/(?P<phid>[^/]+)/' => 'PhabricatorFileInfoController',
-        'proxy/' => 'PhabricatorFileProxyController',
+        'imageproxy/' => 'PhabricatorFileImageProxyController',
         'transforms/(?P<id>[1-9]\d*)/' =>
           'PhabricatorFileTransformListController',
         'uploaddialog/(?P<single>single/)?'
diff --git a/src/applications/files/controller/PhabricatorFileImageProxyController.php b/src/applications/files/controller/PhabricatorFileImageProxyController.php
new file mode 100644
--- /dev/null
+++ b/src/applications/files/controller/PhabricatorFileImageProxyController.php
@@ -0,0 +1,94 @@
+<?php
+
+final class PhabricatorFileImageProxyController
+  extends PhabricatorFileController {
+
+  public function shouldAllowPublic() {
+    return true;
+  }
+
+  public function handleRequest(AphrontRequest $request) {
+
+    $show_prototypes = PhabricatorEnv::getEnvConfig(
+      'phabricator.show-prototypes');
+    if (!$show_prototypes) {
+      throw new Exception(
+        pht('Show prototypes is disabled.
+          Set `phabricator.show-prototypes` to `true` to use the image proxy'));
+    }
+
+    $req_data = $request->getRequestData();
+    $img_uri = $req_data['uri'];
+
+    // Check if we already have the specified image URI downloaded
+    $cache = new PhabricatorKeyValueDatabaseCache();
+    $cache = new PhutilKeyValueCacheProfiler($cache);
+    $cache->setProfiler(PhutilServiceProfiler::getInstance());
+    $cache_key = 'file.imageproxy:'.$img_uri;
+    $result = $cache->getKey($cache_key);
+    if ($result) {
+      return id(new AphrontRedirectResponse())
+        ->setIsExternal(true)
+        ->setURI($result);
+    }
+
+    // Cache missed so we'll need to validate and download the image
+    PhabricatorEnv::requireValidRemoteURIForLink($img_uri);
+    $uri = new PhutilURI($img_uri);
+    $proto = $uri->getProtocol();
+    if (!in_array($proto, array('http', 'https'))) {
+      throw new Exception(
+        pht('The provided image URI must be either http or https'));
+    }
+
+    $viewer = $request->getViewer();
+    try {
+      // Rate limit outbound fetches to make this mechanism less useful for
+      // scanning networks and ports.
+      PhabricatorSystemActionEngine::willTakeAction(
+        array($viewer->getPHID()),
+        new PhabricatorFilesOutboundRequestAction(),
+        1);
+
+      $unguarded = AphrontWriteGuard::beginScopedUnguardedWrites();
+      $file = PhabricatorFile::newFromFileDownload(
+        $uri,
+        array(
+          'viewPolicy' => PhabricatorPolicies::POLICY_NOONE,
+          'canCDN' => true,
+        ));
+      if (!$file->isViewableInBrowser()) {
+        $mime_type = $file->getMimeType();
+        $engine = new PhabricatorDestructionEngine();
+        $engine->destroyObject($file);
+        $file = null;
+        throw new Exception(
+          pht(
+            'The URI "%s" does not correspond to a valid image file, got '.
+            'a file with MIME type "%s". You must specify the URI of a '.
+            'valid image file.',
+            $uri,
+            $mime_type));
+      } else {
+        $file
+          ->setAuthorPHID($viewer->getPHID())
+          ->save();
+      }
+      unset($unguarded);
+      $cache->setKey($cache_key, $file->getViewURI());
+      return id(new AphrontRedirectResponse())
+        ->setIsExternal(true)
+        ->setURI($file->getViewURI());
+    } catch (HTTPFutureHTTPResponseStatus $status) {
+      throw new Exception(pht(
+        'The URI "%s" could not be loaded, got %s error.',
+        $uri,
+        $status->getStatusCode()));
+    } catch (Exception $ex) {
+      throw new Exception(pht(
+        "The URI '%s' could not be loaded due to the following error:\n %s",
+        $uri,
+        $ex->getMessage()));
+    }
+  }
+}