diff --git a/src/applications/files/markup/PhabricatorImageRemarkupRule.php b/src/applications/files/markup/PhabricatorImageRemarkupRule.php
index 36089dc57e..69e9d6bcf1 100644
--- a/src/applications/files/markup/PhabricatorImageRemarkupRule.php
+++ b/src/applications/files/markup/PhabricatorImageRemarkupRule.php
@@ -1,6 +1,9 @@
 <?php
 
 final class PhabricatorImageRemarkupRule extends PhutilRemarkupRule {
+
+  const KEY_RULE_EXTERNAL_IMAGE = 'rule.external-image';
+
   public function getPriority() {
     return 200.0;
   }
@@ -16,6 +19,7 @@ final class PhabricatorImageRemarkupRule extends PhutilRemarkupRule {
     if (!$this->isFlatText($matches[0])) {
       return $matches[0];
     }
+
     $args = array();
     $defaults = array(
       'uri' => null,
@@ -23,9 +27,10 @@ final class PhabricatorImageRemarkupRule extends PhutilRemarkupRule {
       'width' => null,
       'height' => null,
     );
+
     $trimmed_match = trim($matches[2]);
     if ($this->isURI($trimmed_match)) {
-      $args['uri'] = new PhutilURI($trimmed_match);
+      $args['uri'] = $trimmed_match;
     } else {
       $parser = new PhutilSimpleOptions();
       $keys = $parser->parse($trimmed_match);
@@ -37,16 +42,64 @@ final class PhabricatorImageRemarkupRule extends PhutilRemarkupRule {
         }
       }
       if ($uri_key) {
-        $args['uri'] = new PhutilURI($keys[$uri_key]);
+        $args['uri'] = $keys[$uri_key];
       }
       $args += $keys;
     }
 
     $args += $defaults;
 
-    if ($args['uri']) {
+    if (!strlen($args['uri'])) {
+      return $matches[0];
+    }
+
+    // Make sure this is something that looks roughly like a real URI. We'll
+    // validate it more carefully before proxying it, but if whatever the user
+    // has typed isn't even close, just decline to activate the rule behavior.
+    try {
+      $uri = new PhutilURI($args['uri']);
+
+      if (!strlen($uri->getProtocol())) {
+        return $matches[0];
+      }
+
+      $args['uri'] = (string)$uri;
+    } catch (Exception $ex) {
+      return $matches[0];
+    }
+
+    $engine = $this->getEngine();
+    $metadata_key = self::KEY_RULE_EXTERNAL_IMAGE;
+    $metadata = $engine->getTextMetadata($metadata_key, array());
+
+    $token = $engine->storeText('<img>');
+
+    $metadata[] = array(
+      'token' => $token,
+      'args' => $args,
+    );
+
+    $engine->setTextMetadata($metadata_key, $metadata);
+
+    return $token;
+  }
+
+  public function didMarkupText() {
+    $engine = $this->getEngine();
+    $metadata_key = self::KEY_RULE_EXTERNAL_IMAGE;
+    $images = $engine->getTextMetadata($metadata_key, array());
+    $engine->setTextMetadata($metadata_key, array());
+
+    if (!$images) {
+      return;
+    }
+
+    foreach ($images as $image) {
+      $args = $image['args'];
+
       $src_uri = id(new PhutilURI('/file/imageproxy/'))
-        ->setQueryParam('uri', (string)$args['uri']);
+        ->setQueryParam('uri', $args['uri']);
+
       $img = $this->newTag(
         'img',
         array(
@@ -55,9 +108,8 @@ final class PhabricatorImageRemarkupRule extends PhutilRemarkupRule {
           'width' => $args['width'],
           'height' => $args['height'],
         ));
-      return $this->getEngine()->storeText($img);
-    } else {
-      return $matches[0];
+
+      $engine->overwriteStoredText($image['token'], $img);
     }
   }
 
@@ -66,4 +118,5 @@ final class PhabricatorImageRemarkupRule extends PhutilRemarkupRule {
     // If it does, we'll try to treat it like a valid URI
     return preg_match('~^https?\:\/\/.*\z~i', $uri_string);
   }
+
 }