This functionality is supported in the iOS Safari browser.  

Starting with API 18/Android 4.3 there is an intent parameter to allow multiple file selection so this should now be possible. The Google Photos app definitely supports multiple image selection with this intent parameter for ACTION_GET_CONTENT.

https://developer.android.com/reference/android/content/Intent.html#EXTRA_ALLOW_MULTIPLE

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/98dd29fe9a7564ce1e5104df87d769fe2a740a83

commit 98dd29fe9a7564ce1e5104df87d769fe2a740a83
Author: peter@chromium.org <peter@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98>
Date: Wed Aug 06 16:04:35 2014

Allow <input type="file" multiple /> to be used on Android JB MR2+.

Android JellyBean MR2 (API 18) introduced an Intent extra which tells the
file picker that it can select multiple files. Each of the files will be
returned as a ClipData entry on the completed Intent.

BUG= 348912 

Review URL: https://codereview.chromium.org/443683002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@287777 0039d316-1c4b-4281-b951-d872f2087c98

------------------------------------------------------------------
r287777 | peter@chromium.org | 2014-08-06T16:04:35.408748Z

Changed paths:
   M http://src.chromium.org/viewvc/chrome/trunk/src/chrome/android/javatests/src/org/chromium/chrome/browser/input/SelectFileDialogTest.java?r1=287777&r2=287776&pathrev=287777
   M http://src.chromium.org/viewvc/chrome/trunk/src/ui/android/java/src/org/chromium/ui/base/SelectFileDialog.java?r1=287777&r2=287776&pathrev=287777
   M http://src.chromium.org/viewvc/chrome/trunk/src/ui/shell_dialogs/select_file_dialog_android.cc?r1=287777&r2=287776&pathrev=287777
   M http://src.chromium.org/viewvc/chrome/trunk/src/ui/shell_dialogs/select_file_dialog_android.h?r1=287777&r2=287776&pathrev=287777

Allow <input type="file" multiple /> to be used on Android JB MR2+.

Android JellyBean MR2 (API 18) introduced an Intent extra which tells the
file picker that it can select multiple files. Each of the files will be
returned as a ClipData entry on the completed Intent.

BUG= 348912 

Review URL: https://codereview.chromium.org/443683002
-----------------------------------------------------------------

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/229a8308a5ad5f3ec6c2585fabcdb5f23342c303

commit 229a8308a5ad5f3ec6c2585fabcdb5f23342c303
Author: peter@chromium.org <peter@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98>
Date: Thu Aug 07 16:30:06 2014

Add a @TargetApi annotation to SelectFileDialog.onIntentCompleted.

The Intent.getClipData() method is only available in JellyBean MR2 and
higher. The code does a correct version check, but the lint checker is
not satisfied with this check.

BUG= 401333 , 348912 

Review URL: https://codereview.chromium.org/447253002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@288074 0039d316-1c4b-4281-b951-d872f2087c98

------------------------------------------------------------------
r288074 | peter@chromium.org | 2014-08-07T16:30:06.507519Z

Changed paths:
   M http://src.chromium.org/viewvc/chrome/trunk/src/ui/android/java/src/org/chromium/ui/base/SelectFileDialog.java?r1=288074&r2=288073&pathrev=288074

Add a @TargetApi annotation to SelectFileDialog.onIntentCompleted.

The Intent.getClipData() method is only available in JellyBean MR2 and
higher. The code does a correct version check, but the lint checker is
not satisfied with this check.

BUG= 401333 , 348912 

Review URL: https://codereview.chromium.org/447253002
-----------------------------------------------------------------

Fixed. Thanks for the report! :-)

Is this really fixed ? In my tests I still could not get it to work.

http://caniuse.com/#feat=input-file-multiple also references this as unsupported.

As it is, I can use the "multiple" attribute and select multiple files in the intent, yet only one is actually added on the input.

Hello,

It seems that selecting multiple images works only if the files are available locally on the phone. If they are stored in Google Photos and you select multiple images only the first is returned to input.